Tokyo, December 14, 2006 -- Toshiba Corporation, Sony Corporation and NEC Electronics Corporation today announced the successful co-development of an LSI mass production platform for next-generation 45 nanometer (nm) process technology. The new platform integrates elemental breakthroughs with cutting-edge technologies to achieve a highly efficient process for production of high performance system LSI. This technology was unveiled on December 13 (US Pacific Standard Time) at Session 27.2 of the 2006 International Electron Devices Meeting (IEDM) in San Francisco, CA.
The key elements of the new platform are a fully renovated MOSFET integration scheme, and a hybrid structure with a low dielectric constant (low-k) film that assures high performance and reliability.
The MOSFET integration process applies strained silicon technology to the transistor, utilizing crystal lattice distortion to induce performance-boosting local strain at key locations. Optimization of the strain boosts transistor performance to a level 30% faster than that achieved in the present generation of technology.
Application of a low-k film in the intermediate metal layer of the chip during the back-end process reduces parasitic capacitance and improves circuit performance. The three partners confirmed a dielectric gate film with an effective 15-year lifetime, a span surpassing the average lifetime of a high performance LSI. They also carried out exhaustive tests of the platform and proved a layer yield of over 98% for the challenging back-end process, confirming that the technology achieves the reliability essential for mass production.
In addition, the partners have led the industry in applying immersion lithography technology with an ultra-high numerical aperture (NA) of over 1.0 to formation of the transistor node, achieving a cell with an area of 0.248 micron m2 in an ultra high density SRAM. The new cell is the smallest yet achieved.
The three companies are simultaneously developing two 45nm processes -- the current platform, which is ideal for high performance LSIs, as well as a platform for applications with low power consumption requirements, which is expected to be completed in early 2007.
Outline of development
The high performance 45nm platform technology optimizes a balance of high performance and high reliability while combining individual elemental technology with new technologies and improvements. The specific technology elements are as follow.
1. Optimal processing conditions based on basic technology
(1) Optimizing application of strained silicon technology
Strained silicon technology enhances carrier mobility. In the new process, stress film is formed on the source/drain integration as well as the upper part of the transistors, a solution that enhances the strain effect and contributes to optimized transistor performance. The result is an improvement of over 30% in transistor performance as a whole, with an improvement in transistor drive current of over 20% and 60% in the nMOS and pMOS transistor modes, respectively.
Application of strained silicon technology and performance improvement
Upper transistor part
Source and drain Part
High stress tensile liner
more than 20%
High compressive liner
more than 60%
(2) Optimizing back-end process technology
In the back-end process, the LSI interconnect layer is formed with a hybrid dual-damascene structure, with optimized porous low-k films applied to both the interconnect layer and the via layer. This approach enhances control of the interconnect profile. Optimization of the manufacturing process achieves an effective dielectric constant (keff=2.7) at the level required for 45nm generation performance. Tests have confirmed a layer yield of more than 98%, an excellent level on a test structure, matching actual production, and also confirmed circuit performance reliability.
2. High accuracy processing with ultra high NA immersion lithography
The companies confirmed the effectiveness of applying ultra high NA (over 1.0) immersion lithography. Contact holes were accurately controlled and formed to the expected size on an ultra-high-density SRAM (UHD-SRAM), meeting highly demanding tolerances for the LSI's internal structure. The process confirms that there are no problems with accuracy in applying ultra high NA immersion lithography to every circuit.
Fig. Contact holes on an UHD-SRAM processed with dry lithography vary widely (left), whereas there are few variations with ultra high NA immersion lithography (right).
- Strained silicon technology enhances the carrier mobility of transistor devices by utilizing crystal lattice distortion. A primary method is inducing local strain that forms a stress liner on top of transistor elements. In MOSFET, tensile stress and compressive stress are added to the nMOS and to pMOS, respectively.
- Low-k film is a low-dielectric-constant film used in the back-end process after forming transistors in the LSI manufacturing process. It reduces parasitic capacitance between the interconnect layers and so enhances performance. In general, low-k materials can cause deterioration in device solidity and are difficult to manufacture.
- Immersion lithography technology is a resolution enhancement technique that interposes a liquid medium between the optics and the wafer surface, replacing the usual air gap. It increases the numerical aperture (NA) of lens to a value greater than one, the limit that can be achieved with an air gap.