An insulator-lined silicon substrate-via technology with high aspect ratio

Abstract

We have developed a novel high-aspect ratio substrate-via technology in silicon that features a SiN insulator liner. In this technology, the via is completely filled with electroplated Cu. We have demonstrated vias with an aspect ratio of 30 and we have verified the integrity of the liner in vias with an aspect ratio of 8. The impedance of individual vias was measured in the microwave regime using a high-frequency test structure. The measured inductance of vias with aspect ratios between 3 and 30 approach the theoretically expected values.

A Through-Wafer Interconnect in Silicon for RFICs

“…Substrates had a resistivity of [10][11][12][13][14][15][16][17][18][19][20] cm. In the following paragraphs, we give details about each of the key process steps in our technology.…”

“…Early results of this technology characterized up to 6 GHz were published in [13]. This paper discusses the details of the fabrication process of the substrate vias and gives more extensive results of isolated vias and Faraday cages up to 50 GHz.…”

An equivalent circuit model for a Faraday cage substrate crosstalk isolation structure

“…4). The lumped-element values used in simulations are listed in Table 1 spread in isolation effectiveness that we observe from sample to sample can be easily accommodated by just varying R v and L v in a manner consistent with the spread measured in [5]. This variation in the via inductance and resistance can be attributed to fabrication issues in contacting the via at the surface.…”

“…The experimental work has been described in detail in [4] and [5]. Substrate isolation was measured between a pad located inside the cage (transmitter) and another outside (receiver) at distances between 100 and 200 µm in a ground-signal-ground configuration (Fig.…”

“…1) [4]. This Faraday cage uses high-aspect ratio, through-wafer vias with a silicon nitride liner and a solid copper core that is shorted at the top and to the ground plane at the back of the wafer [5]. Faraday cages have shown an isolation improvement of 41 dB at 1 GHz, 30 dB at 10 GHz, and 16 dB at 50 GHz for a separation distance of 100 µm when compared to a reference structure [4].…”