TSMC (Taiwan Semiconductor Manufacturing Co Ltd) made an announcement about its slim-type glass interposer that is as large as a 300mm wafer at International Electron Devices Meeting (IEDM) 2013, which runs from Dec 9 to 11, 2013, in Washington, D.C. (lecture number: 13.4).
The title of the lecture was "300mm Size Ultra-thin Glass Interposer Technology and High-Q Embedded Helical Inductor (EHI) for Mobile Application."
As it is difficult to further scale process technology, the importance of 2.5-dimension (2.5D) chip technology, which stacks multiple chips on a silicon (Si) interposer, is growing. However, because Si interposers are expensive, they are currently used only for FPGAs for high-end applications, etc. Moreover, Si causes a large loss in the high-frequency range.
On the other hand, there is enough infrastructure to mass-produce large-size glass substrates, making it easy to lower costs. And glass shows excellent properties in the high-frequency range. The glass interposer announced by TSMC is expected to be applied to 60GHz-band WiFi systems, etc.
Many of the glass interposers that have been announced thus far have a size of 150mm. Their thicknesses range from 175-250μm. And the electrodes (TGVs) that penetrate the glass interposers are 30-35μm in diameter.
This time, TSMC used a 300mm glass wafer with a glass thickness of 50μm. The diameter of its TGV is 25μm. After attaching the glass wafer to a Si carrier, reducing the thickness of the glass to 50μm and forming through-holes, TGVs were formed by copper (Cu) plating and chemical mechanical polishing (CMP).
When a 2D spiral inductor was formed using the new glass interposer, its Q factor was 20 or higher in the frequency range of 1G to 5GHz. A spiral inductor formed on a Si interposer had a Q factor of 18 or less. With the Si interposer, the maximum value of the Q factor was 25 or less. On the other hand, with the glass interposer, it was 30 or higher. The 2D spiral inductor was formed using the two-layer wiring on the surface of the glass interposer.