1,720,968 research outputs found
Adverse effect of Ge+ implantation for fabrication of SiGe PMOS
No full textSiGe heterostructure MOSFETS have the potential for improved channel mobility over Si only devices. It is shown that fabrication by implantation leads to inferior devices in contrast to previously reported work. A simultaneous decrease of the drain current and increase of the interface state density has been observe
Leakage current mechanisms associated with selective epitaxy in SiGe heterojunction bipolar transistors
No full textSiGe Heterojunction Bipolar Transistors (HBT's) have been fabricated using selective epitaxy for the Si collector, followed in the same growth step by non-selective epitaxy for the SiGe base and Si emitter cap. E/B leakage currents are compared with cross section TEM images to identify sources of leakage currents associated with the epitaxy. In addition, the influence of the position of the extrinsic base implant with respect to the polysilicon emitter on the leakage currents is studied. The emitter/base leakage currents are modelled using Shockley-Read-Hall recombination, trap-assisted tunnelling and Poole-Frenkel generation. The position of the extrinsic base implant is shown to have a strong influence on the leakage currents. The Poole-Frenkel effect dominates the emitter/base leakage current in transistors in which the collector area is smaller than the polysilicon emitter. This result is explained by penetration of the emitter/base depletion region into the p+ polysilicon extrinsic base at the perimeter of the emitter. These leakage currents are eliminated when the collector area is increased so that the extrinsic base implant penetrates into the single-crystal silicon at the perimeter of the emitter
SiGe device architectures synthesised by local area Ge implantation; structural and electrical characterisation
No full textSiGe device islands have been synthesised by Ge+ ion implantation of doses of 0.45 x 1016 Ge+/cm2 to 4.05 x10 Ge+/cm2 at 100keV or 200keV into patterned (100) bulk silicon wafers. The control of 'mask edge defects' and 'end of range' defects has been achieved by applying Si+ post-amorphisation, where the ions are implanted into a wider window, and by using solid phase epitaxial regrowth. Defect free SiGe alloy islands with a peak Ge concentration of ~6at% and minority carrier generation lifetimes comparable to bulk silicon (~ms) have been successfully produced. The integration of this synthesis process into CMOS and bipolar technologies is discussed. Realization of shallower islands, with dimensions more consistent with future generations of advanced devices and with higher Ge contents, is in hand
A comparison of pnp and npn SiGe HBTs fabricated by Ge implantation
No full textA study is made of npn and pnp SiGe HBTs produced using Ge implantation. The Ge is implanted into a complementary bipolar process after active area definition. Increased collector currents are observed in both npn and pnp transistors due to the presence of the Ge. The implanted Ge has opposing effects on the emitter dopant diffusion: increasing the arsenic diffusion coefficient in the npn devices and decreasing the boron diffusion coefficient in the pnp devices
Suppression of boron transient enhanced diffusion in silicon and silicon germanium by fluorine implantation
No full textIn this paper, a study is made of the effect of fluorine implantation on boron transient enhanced diffusion in Si and SiGe by characterising the diffusion of boron marker layers in Si and SiGe in samples with and without a 288 keV, 6x10^13 cm-2 P+ implant and with and without a 185 keV, 2.3x10^15 cm-2 F+ implant. It is shown that fluorine implantation totally eliminates boron transient enhanced diffusion caused by the phosphorus implant as well as significantly reduces boron thermal diffusion in both Si and SiGe. Fluorine SIMS profiles for both Si and SiGe samples show the presence of a shallow peak in the vicinity of the boron marker layer and a deep peak close to the range of the fluorine implant. Cross-sectional transmission electron micrographs show the presence of a band of dislocation loops that correlates with the position of the deep fluorine peak, but no defects are present in the position of the shallow fluorine peak. It is proposed that the shallow fluorine peak is due to vacancy-fluorine clusters that are too small to resolve by TEM. The role of the vacancy-fluorine clusters and the dislocation loops on the suppression of boron diffusion in Si and SiGe is discussed
Electrical and Materials Characterisation of GSMBE Grown Si1-x-yGexCy Layers for Heterojunction Bipolar Transistor Applications
No full textThis paper reports on detailed materials and electrical characterization of strain-compensated Si1?x?yGexCy layers synthesized by gas source molecular beam epitaxy (GSMBE). Materials assessment included the application of spectroscopic ellipsometry (SE), x-ray diffraction (XRD) and high-resolution cross-section transmission electron microscopy (HRXTEM). An almost fully strain-compensated Si0.88Ge0.11C0.01 alloy with high substitutional carbon incorporation (XRD) and well-defined structure with coherent interfaces (HRXTEM) was produced. An increase of C content (up to 1.6%) resulted in a tensile strained SiGeC alloy and degraded electrical characteristics. The minority-carrier lifetime is a parameter strongly dependent on mid-gap energy band levels, which determine the leakage currents in heterojunction bipolar transistors, and it was assessed here using the capacitance-transient technique. Metal–oxide–semiconductor (MOS) test capacitors were fabricated on Si/SiGe/Si and Si/SiGeC/Si structures using low-temperature plasma oxidation for dielectric growth. The strain-free Si0.88Ge0.11C0.01 layers exhibit a minority-carrier lifetime, ?g, of ?0.1–0.2 µs which constitutes degradation of the carrier lifetime by two orders of magnitude compared to control SiGe layers. The obtained range of ?g is nevertheless sufficient for the successful application of epitaxial strain-compensated SiGeC layers in high performance heterojunction bipolar transistors (HBTs)
Regrowth behaviour of SiGe/Si structures formed by Ge+ Ion implantation and post amorphisation
No full textSiGe Heterojunction Bipolar Transistors on Bonded SOI Incorporating Buried Silicide Layers
No full textA technology is described for fabricating SiGe Heterojunction Bipolar Transistors (HBTs) on wafer bonded SOI substrates that incorporate buried tungsten silicide layers for collector resistance reduction or buried groundplanes for crosstalk suppression. The physical structure of the devices is characterized using cross-section TEM, and the electrical properties of the buried tungsten silicide layer are characterized using sheet resistance measurements as a function of bond temperature. Possible contamination issues associated with the buried tungsten silicide layer are investigated by measuring the collector/base reverse diode characteristics. A resistivity of 50ohm.cm is obtained for the buried silicide layer for a bond anneal of 120mins at 1000C. Collector/base reverse diode characteristics show a voltage dependence of approximately V1/2, indicating that the leakage current is due to Shockley-Read-Hall generation in the depletion region. Fitting of the current/voltage characteristics gives a generation lifetime of 90ns, which is as expected for the collector doping of 7x1017cm-3. These results indicate that the buried tungsten silicide layer does not have a serious impact on junction leakage
Effect of Fluorine Implantation Dose on Boron Transient Enhanced Diffusion and Boron Thermal Diffusion in Si1-xGex
No full textThis paper studies how boron transient enhanced diffusion (TED) and boron thermal diffusion in Si1-xGex are influenced by a high-energy fluorine implant at a dose in the range 5 × 1014 cm-2 to 1 × 1016 cm-2. Secondary ion mass spectroscopy (SIMS) profiles of boron marker layers are presented for different fluorine doses and compared with fluorine SIMS profiles and transmission electron microscopy (TEM) micrographs to establish the conditions under which boron diffusion is suppressed. The SIMS profiles show that boron thermal diffusion is reduced above a critical F+ dose of 7-9 × 1014 cm-2, whereas boron TED is suppressed at all doses. Fitting of the measured boron profiles gives suppressions of boron TED diffusion coefficients by factors of 6.8, 10.6, and 12.9 and of boron thermal diffusion coefficient by factors of 1.9, 2.5, and 3.5 for F+ implantation doses of 9 × 1014, 1.4 × 1015, and 2.3 × 1015 cm-2 respectively. The reduction of boron thermal diffusion above the critical fluorine dose correlates with the appearance of a shallow fluorine peak on the SIMS profile in the vicinity of the boron marker layer, which is attributed to vacancy-fluorine clusters. This reduction of boron thermal diffusion is explained by the effect of the clusters in suppressing the interstitial concentration in the Si1-xGex layer. The suppression of boron TED correlates with a deep fluorine peak around the range of the fluorine implant and TEM micrographs show that this peak is due to a band of dislocation loops. This suppression of boron TED is explained by the retention of interstitials in the dislocation loops, which suppresses their backflow to the surface. The fluorine SIMS profiles show that the fluorine concentration in the Si1-xGex layer increases with increasing germanium concentration and that the fluorine concentration in the Si1-xGex layer after anneal is much higher than after implant. This indicates that fluorine is transported into the Si1-xGex layer from the adjacent silicon, and is explained by the lower formation energy for vacancies in Ge than in Si. This accumulation of fluorine in the Si1-xGex layer during anneal is advantageous for devices like SiGe heterojunction bipolar transistors, where the boron must be kept within the Si1-xGex layer. © 2005 IEEE
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