Philips Develops Fastest Silicon BiCMOS Process

-- Semiconductor International, 1/1/1999

Philips Semiconductors (Eindhoven, The Netherlands) has announced a silicon BiCMOS process technology that can be used to produce devices with f_max values of ~70 GHz. This is roughly 2X typical values previously achieved for silicon production devices and is comparable with those of SiGe and GaAs ICs. Philips estimates the new process can be used to fabricate devices at about 2/3 the cost of SiGe and GaAs products.

This new QUBiC3 process can integrate high-frequency RF bipolar circuits with high-speed CMOS logic blocks onto a single chip. Philips plans to use it to produce a new range of high-speed, high-reliability RF front-end ICs that are scheduled for release in 1999. The company claims these products will enable it to maintain a leading position in the aggressive mobile telecommunications market.

The CMOS part of the QUBiC3 process currently employs a mature 0.5 µm process with 0.42 µm effective gate lengths. It is supported by a comprehensive set of design libraries and tools. An improved double polysilicon technology is used in the bipolar section of the circuit, which has an effective emitter geometry of <0.3 µm. It uses a self-aligned silicide and a low-capacitance interconnect system.

The fourth metal layer used in QUBiC3 devices allows designers to build 'on-chip' inductors, thus delivering higher levels of integration at lower cost.

Hydrogen silesquioxane (HSQ), which has a low dielectric constant of 3.0, is used as the insulating material between metal layers formed in the QUBiC3 process. The use of HSQ insulation results in a 45% reduction in stray capacitance relative to use of conventional insulating materials that have a dielectric constant of ~4.0. The reduction in parasitic capacitance is vital for achieving optimum high-frequency performance. Philips claims this unique feature, combined with the ability to achieve extremely high-speed switching and a very low noise figure of only 0.6 dB means that QUBiC3 is the ideal process to make ICs for low noise amplifier designs and mobile telecommunications applications. Its low noise and distortion are claimed to match the best offered by SiGe and GaAs.

Higher speeds and improved functionality are achieved by optimizing the mix of CMOS and bipolar circuitry. High quality passive components can provide enhanced design flexibility and systems integration that can be used to produce, for example, lighter, more compact and less costly phone systems. High speed is obtained using 3 V supplies and very low operating currents, so battery life is extended. Other applications for the technology are foreseen in television, paging and video teleconferencing. As it can handle video data rates, it makes wrist watch size video phones possible in the near future at reasonable cost.

The process can integrate a wide range of resistors and capacitors on a chip, while providing good matching for high yields and ease of manufacture. A thick fourth metal layer has been developed and optimized for the fabrication of high-performance inductors (see Figure). This enables higher levels of integration to be obtained together with much lower costs. On-chip inductors with Q factors exceeding 20 are easily achieved as well as on-chip tunable inductance-capacitance filters.

Philips claims complex SiGe technologies, which may be limited to just two metal interconnect layers, can require up to 30 masking layers for fabrication. However, the same performance with 2X as many layers of interconnect can be obtained using QUBiC3 and just 26 masking stages in silicon. Work has now started on a 0.25 µm QUBiC4 process that aims to achieve an f_max of 90 MHz.