Akihiro Kodama

HCl-free selective epitaxial Si-Ge growth by LPCVD for high-frequency HBTs

Low-temperature HCl-free selective silicon germanium epitaxial growth using low-pressure chemical vapor deposition was developed. By utilizing the incubation period of the poly-SiGe growth on SiO/sub 2/, sufficient selectivity was obtained without the use of HCl gas. The advantages of this HCl-free process are sufficient growth rate at low temperature (660/spl deg/C) and capability of high-concentration boron doping without surface roughening. The thickness uniformity of the selectively grown layers throughout a wafer was good and the local loading effect did not appear. These results show the process can be used for fabricating heterojunction bipolar transistors (HBTs). The HBTs fabricated using the process have excellent yields and high-frequency characteristics, that is, 80-GHz cutoff frequency and 160-GHz maximum oscillation frequency. These characteristics and good uniformity of cutoff frequency throughout a wafer show that developed selective growth process can be applied to production of SiGe HBTs.

High-speed scaled-down self-aligned SEG SiGe HBTs

A scaled-down self-aligned selective-epitaxial-growth (SEG) SiGe HBT, structurally optimized for an emitter scaled down toward 100 nm, was developed. This SiGe HBT features a funnel-shaped emitter electrode and a narrow separation between the emitter and base electrodes. The first feature is effective for suppressing the increase of the emitter resistance, while the second one reduces the base resistance of the scaled-down emitter. The good current-voltage performance - a current gain of 500 for the SiGe HBT with an emitter area of 0.11 /spl times/ 0.34 /spl mu/m and V/sub BE/ standard deviation of less than 0.8 mV for emitter width down to about 0.13 /spl mu/m - demonstrates the applicability of this SiGe HBT with a narrow emitter. This SiGe HBT demonstrated high-speed operation: an emitter-coupled logic (ECL) gate delay of 4.8 ps and a maximum operating frequency of 81 GHz for a static frequency divider.

A variable inductor using mutual-current control and application to a SiGe 4.5-GHz VCO for wide tuning range

A novel variable inductor using mutual current control was developed and applied to a 4.5-GHz SiGe voltage controlled oscillator (VCO). It consists of a primary inductor, a secondary inductor, and a variable capacitor, and its inductance can be tuned by adjusting the capacitance of the capacitor. It was designed for application to a proposed 4.5-GHz VCO in 0.25-/spl mu/m SiGe BiCMOS technology. It exhibited a large inductance variation of 22% and a high quality factor of 24 at 4.5 GHz in electro-magnetic simulation. The VCO has a 1.2-GHz tuning range, 32% wider than that of a conventional VCO, and a low phase noise of -121.8 dBc/Hz (at a 1-MHz offset frequency).

Promoting emitter diffusion process and optimization of vertical profiles for high-speed SiGe HBT/BiCMOS

A high-temperature anneal-resistant process, which enables high-speed SiGe HBTs to embed scaled CMOS, is optimized in SiGe BiCMOS technology. This process, called promoting emitter diffusion (PED), is based on enhanced phosphorous diffusion from poly-Si emitter electrodes at high temperature to fabricate thin base layers and shorten the base transit time. By investigating the dependence of high-frequency performance on diffusion temperature, as-grown base layer thickness, and Si cap thickness, the methodology for PED optimization was yielded. In addition, this PED process is effective in reducing an extrinsic base resistance due to deep boron diffusion from poly-Si base electrodes. This indicates that the PED process is very effective at improving the tradeoff relationship between cutoff frequency f/sub T/ and maximum oscillation frequency f/sub max/ in self-aligned SiGe HBTs using selective epitaxial growth. As a consequence, both f/sub T/ and f/sub max/ of more than 200GHz were successfully obtained.

Suppression of B Outdiffusion by C Incorporation in Ultra-High-Speed SiGeC HBTs

The effect of incorporated C on preventing the diffusion of B in selectively grown Si1-x-yGexCy layers has been studied. The diffusivity of B was significantly decreased by increasing the C content, even when the concentrations of B were high. Furthermore, self-aligned SiGeC heterojunction bipolar transistors (HBTs) were fabricated, and the effects of incorporating C in the base layer on device performance were evaluated. A shallower base with a higher concentration of B was produced by suppression the B outdiffusion. Consequently, low values for base resistance and a high cutoff frequency of 168 GHz were achieved with a 4-nm-thick p-Si1-x-yGexCy layer where the C content was 0.2% and the B concentration was 1×1020 cm-3.

A simplified distribution parasitic capacitance model for on-chip spiral inductors

A modeling methodology for determining simply distributed parasitic capacitances used in a lumped equivalent circuit of silicon monolithic spiral inductors is proposed. To calculate the capacitances for the obtained model, the degeneration factors for the total amount of distributed parasitic-capacitances are introduced. A Q-factor modeling-error of less than 9.4% was obtained by comparing the measured and modeled characteristics in the microwave region