Technologies and market for 2.5D interposers
Last year Xilinx, a world-leading provider of All-Programmable FPGAs, SoCs and 3D ICs, and its technology and manufacturing partner Taiwan Semiconductor Manufacturing Company (TSMC) developed a high-κ metal gate (HKMG), high-performance, low-power 28-nm process technology for FPGAs. TSMC announced that it would provide full manufacturing and assembly support for 2.5D and 3D IC designs.
According to Mike Santarini of Xilinx, 2.5D has marked advantages of capacity, performance, system space and overall system power consumption over traditional single-die implementations. The vision of a 3D IC is truly promising, but some industry watchers believe the 2.5D market is perhaps being too easily dismissed as a stepping stone to true 3D design. 2.5D has the distinct advantage of being already here today for some companies — and leveraging it takes only minor adjustments to current design flows and, seemingly, the manufacturing chain.
As 2.5D packaging has become the fastest growing packaging segment, because of its performance and economic advantages, interposer substrates are one of the most critical components to increase the applications of 2.5D packaging. The main material of the interposer today is silicon, while both glass and organic substrates have been increasingly considered as promising alternatives.
Lighting-edge packaging solutions from USHIO
Since it was established in 1964, USHIO INC. has been delivering to the global semiconductor industry UV lamps for photolithography processes, VUV lamps for surface improvement, and halogen lamps for thermal processes.
Starting with these light sources, USHIO has expanded its proprietary application technologies based on development of new light sources and lighting-edge technologies. It has developed, manufactured, and marketed a wide range of lithography systems for advanced packaging (fine-printed circuit boards), wafer-level packaging (WLP), MEMS, LEDs, and power devices — all of which are the focus of attention in the semiconductor fabrication arena.
Recently, USHIO has been focusing on 2.5D packaging to develop its UX5 panel stepper and Square 70 interposer stepper systems as well as the Align 600 maskless scanner system for fan-out WLP.
By providing reliable yet high-performance lithography tools, USHIO has made a great contribution to the high-volume production of such advanced packages as above while achieving significant cost reduction in the manufacturing of high-end digital products including smartphones, tablet PCs, and other mobile devices.
2.5D interposer stepper system Square 70
In recent years, leveraging its lighting-edge technologies including light sources, optics, and mechanical engineering, USHIO has developed the lithography systems used for fabricating interposers indispensable for 2.5D devices.
Square 70 stepper system (Courtesy of Ushio)
Perfect lithography for glass and organic interposers as well as Si
Two of the highest hurdles for high-volume production of 2.5D devices are enabling single-shot exposure of a larger substrate as well as using of lower-cost organic and glass substrates. In order to clear these hurdles, USHIO developed the Square 70, the latest model of its interposer stepper series.
In July 2013, USHIO delivered the first unit of the Square 70 large-field stepper system to one of its main users. Backed by an increase in capital investment of device manufacturers for 2.5D integration, the Square 70 has been running at a 2.5D pilot line where it has proved by its outstanding performance to be usable for High Volume Manufacturing (HVM) in the near future.
The Square 70 stepper system has achieved an industry-leading resolution of 2 µm L/S on a glass or organic substrate as well as a 300-mm Si wafer. Mounted with a proprietary alignment mechanism, the Square 70 is able to address a warp or the expansion/contraction of an organic substrate. It thus is optimum for manufacturing 2.5D/3D interposers made of organic substrates that have recently become popular, in addition to Si wafers.
USHIO installed one unit of a Square 70 based projection aligner dedicated to developing 2.5D glass substrate at the Georgia Tech 3D Systems Packaging Research Center (GT-PRC) on October 31 in 2013, based on conclusion of the partnership agreement related to the interposer development consortium sponsored by GT-PRC. USHIO has already dispatched its engineer and started supporting development of lower-cost glass interposers and packages. USHIO is now aggressively developing the lithography technology, dedicated to 2.5D and 3D glass and organic interposers, including testing of exposure on large and thin glass substrate as well as achievement of the target resolution required to achieve these finer patterns.
Moreover, with a large lens field of 70 mm x 70 mm, the Square 70 is capable of processing large-size interposers without any stitch at a high throughput and has the flexibility to allow processing of the above three substrate types, thus significantly reducing the cost for manufacturing interposers. There is no other lithography system available yet that can achieve this goal.
In addition, to meet the further need for finer circuit patterns, USHIO is currently developing a large-field precision projection lens that can produce a super-high resolution of 1 µm L/S.
Utilizing this Square 70 stepper allows significant reduction of the interposer manufacturing cost even though the design cost will rise as the device node becomes finer, which ultimately leads to reduction of the manufacturing cost of 2.5D packages for high-performance logic devices.
Toyoharu Inoue is Deputy General Manager of Business Unit I, USHIO INC. He is leading the Exposure Process Equipment & Light Source Division and responsible for marketing, product development and sales. He joined USHIO INC. in 1985 as an engineer in the Power Supply Division; he worked with Gigaphoton Inc., a former joint venture of USHIO and KOMATSU, from 2000 through 2006, where he marketed high-power excimer laser light sources for lithography processes. He returned to USHIO INC. in 2007, and in 2008 started leading the exposure equipment business, making a great contribution to marketing of the panel stepper “UX-5” for HVM of advanced FC-BGA packages.