B. Barbalat

230-GHz self-aligned SiGeC HBT for optical and millimeter-wave applications

This paper describes a 230-GHz self-aligned SiGeC heterojunction bipolar transistor developed for a 90-nm BiCMOS technology. The technical choices such as the selective epitaxial growth of the base and the use of an arsenic-doped monocrystalline emitter are presented and discussed with respect to BiCMOS performance objectives and integration constraints. DC and high-frequency device performances at room and cryogenic temperatures are given. HICUM model agreement with the measurements is also discussed. Finally, building blocks with state-of-the-art performances for a CMOS compatible technology are presented: A ring oscillator with a minimum stage delay of 4.4 ps and a 40-GHz low-noise amplifier with a noise figure of 3.9 dB and an associated gain of 9.2 dB were fabricated.

230 GHz self-aligned SiGeC HBT for 90 nm BiCMOS technology

This paper describes a 230 GHz self-aligned SiGeC HBT featuring a selective epitaxial base and an arsenic-doped monocrystalline emitter. These technical choices are presented and discussed with respect to BiCMOS performance objectives and integration constraints.

300 GHz f/sub max/ self-aligned SiGeC HBT optimized towards CMOS compatiblity

This paper summarizes the work carried out to improve performances of a SiGeC HBT featuring a selective epitaxial base and an arsenic-doped monocrystalline emitter. A 300 GHz f/sub max/ is reported for a transistor sustaining high thermal budget.

250-GHz self-aligned Si/SiGeC HBT featuring an all-implanted collector

This paper presents investigations led to simplify the collector module of SiGeC HBTs in order to reduce technology cost. Outcome of this work is an HBT featuring an all-implanted collector with record fT and fmax (>250 GHz)

Deep trench isolation effect on self-heating and RF performances of SiGeC HBTs

This paper focuses on the effect of deep trench isolation (DTI) on self-heating and electrical performances of state-of-the-art SiGeC heterojunction bipolar transistors (HBTs). The influence of DTI on the heat dissipation and on the thermal resistance of HBTs is studied both with electrical measurements and simulations. The results show that the DTI has a significant influence on heat dissipation and on the thermal resistance values but only little impact on RF performances.

Carbon effect on neutral base recombination in high-speed SiGeC HBTs

We have presented the performances and electrical behavior of high-speed SiGeC HBTs having enhanced NBR by carbon insertion in excess. The current gain is strongly reduced, so that BVCEO increases by 0.5 V, and the fT times BVCEO product shifts from 340 to 423 GHz.V, which offers new possibilities for HBTs optimization, notably by increasing collector doping. Thanks to the NBR, the current gain dependency with temperature above 300 K is reduced, which is interesting for applications such as power amplifiers. The current gain evolution with VBE is explained by trap saturation, which was confirmed in simulations by inserting a trap level in the base gap. The band gap dependency with carbon insertion is also demonstrated and was developed in the final paper

The effect of carbon on neutral base recombination in high-speed SiGeC heterojunction bipolar transistors

This paper deals with the introduction of high carbon doses in the base of SiGeC HBTs to create neutral base recombination (NBR). The base current IB was increased by a factor of 10, with significant enhancement of the collector-to-emitter breakdown voltage BVCEO. The transit frequency fT was kept nearly constant, which enabled the fT × BVCEO product to be pushed up. The analysis is followed by 1/f noise measurements, temperature analysis and device simulations to demonstrate a trap saturation effect. Electrical bandgap measurements enable us to discern whether carbon is inserted in substitutional or interstitial sites.

Germanium profile, graduality and base doping level influences in the performance of SiGe HBT

In this paper, results are presented for eight samples. The investigated SiGe HBTs are compatible with the CMOS core process. They are based on a double poly-silicon technology (base and emitter), use a fully self aligned architecture (FSA emitter-base and collector-base junctions) and selective base epitaxy (SEG) with carbon incorporation.

Control of Carbon Incorporation in Selectively Grown Epitaxial SiGe:C Layers Dedicated to HBTs

Carbon atoms (C) are now commonly incorporated in advanced SiGe HBTs to reduce base width because, when located in substitutional sites, C atoms efficiently minimize boron diffusion [1]. Selective Epitaxial Growth (SEG) of SiGe:C films are performed in a 200 mm RT-CVD reactor. Selectivity towards silicon nitride is obtained through the addition of HCl. It allows the fabrication of high performances Fully Self-Aligned (FSA) HBTs [2]. SIMS analysis of a SiGe:C/Si multilayer (figure 1.a) shows sharp C profiles. C incorporation is accurately controlled as illustrated by the same C content measured in the first and fourth SiGe:C layers during the growth of which an identical methylsilane (MS) flow was injected in the reactor (note the linear scale). The combined XRD/SIMS characterization (figure 1.b) reveals that 100% of C atoms are in substitutional sites (Cs) up to a total concentration [Ct] = 6.5 × 10 cm. For higher [Ct], a significant part of C atoms are in interstitial sites (Ci). FSA HBTs have been fabricated with 22 nm thick SiGe:C films and various [Ct]. Gummel plots (figure 2) shows that the evolution of the base current (IB) with emitter-base voltage (VBE) is near-to-ideal for the lowest [Ct] value (3.5E19 cm ). For higher [Ct] the IB versus VBE characteristic becomes non ideal especially when VBE reduces. The increase of IB is attributed to the reduction of minority carriers’ lifetime (electrons) through recombination mechanisms within the emitter-base depletion region. When incorporated in interstitial sites, C atoms tend to form extended defects where recombinations may occur. Electrical results highlight that some defects are grown for [Ct] as low as 6.5 × 10 cm. This is in disagreement with the combined XRD/SIMS analysis, meaning that this standard method is not sensitive enough to the presence of Ci in SiGe:C films. In figure 3, the integrated photoluminescence (PL) intensity is reported as a function of [Ct]. For [Ct] lower than 3.5 × 10 cm the PL signal is roughly constant. As soon as [Ct] exceeds 3.5 × 10 cm, PL signal drops and tends to reach 0. We note in figure 3 that PL intensity and IB evolutions are strongly related. This is because both optical and electrical properties are altered by recombinations induced by Ci-related defects. Thanks to the accurate control of C incorporation pointed out in figure 1.a, any specific C profile can be tailored, even at the scale of a few nanometers. This Cengineering is applied to the realization of HBTs having enhanced Neutral Base Recombination (NBR) [3]. Due to its high sensitivity on recombinations, PL is used to select the appropriate [Ct] to be incorporated in each part of the base profile (see insert of figure 4). On one hand, a high [Ct] (named [Ct]NBR) resulting in a poor PL signal, i.e. high probability electrons’ recombination, is used during the growth of the in-situ boron-doped neutral base. On the other hand, an absolutely defect-free material is required in space charge zones (around B-doped SiGe:C) so that [Ct] is fixed to the maximum value that does not degrade PL. Figure 4 shows that IB increases with [Ct]NBR but remains ideal, proving that Ci-related defects were localized in the neutral base. Because IC is almost insensitive to the NBR process, current gain is reduced and BVCEO increases from 1.4 V for standard process to 1.9 V with the use of C-induced NBR. In conclusion, it has been shown that PL is more relevant than XRD and SIMS for the characterization of interstitial carbon in SiGe:C films dedicated to HBTs. This technique has been applied to the development of new HBTs using NBR to improve fT-BVCEO trade-off.