Investigations on Initial Beta Drift During Reliability Test for MOCVD Grown C-doped InGaP/GaAs HBTs (original) (raw)
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Microelectronics Journal, 2001
This work describes the implementation of an experimental procedure to evaluate the reliability of Heterojunction Bipolar Transistors (HBT) on a GaAs substrate. It is based on the separation of aging test accelerating factors applied on two test vehicles: HBT and Transmission Line Model (TLM) structures associated with emitter, base and collector layers. To identify the physical origin of the degradation mechanism, analysis techniques are used: EDX, SEM and TEM observations for which a new sample preparation method has been worked out. Three different technological fabrication processes, are investigated: AlGaAs/GaAs double-mesa HBT, GaInP/GaAs self-aligned HBT and GaInP/GaAs fully planar HBT. These investigations have revealed two major failure mechanisms: the degradation of SiN±GaAs interface correlated with the increase of emitter-to-base leakage current of HBT submitted to combined bias and temperature stresses; the detachment of Ge/Mo/W emitter ohmic contact related to the base and collector current decrease for high level injection in forward regime.
High reliability InGaP/GaAs HBT
IEEE Electron Device Letters, 1998
Excellent long term reliability InGaP/GaAs heterojunction bipolar transistors (HBT) grown by metalorganic chemical vapor deposition (MOCVD) are demonstrated. There were no device failures (T = 10 000 h) in a sample lot of ten devices (L = 6:4 m 2 20 m) under moderate current densities and high-temperature testing (Jc = 25 kA/cm 2 ; Vce = 2.0 V, Junction Temp =264 C). The dc current gain for large area devices (L = 75 m 275 m) at 1 kA/cm 2 at a base sheet resistance of 240 ohms/sq (4 2 10 19 cm 03 @ 700Å) was over 100. The dc current gain before reliability testing (L = 6:4 m 2 10 m) at 0.8 kA/cm 2 was 62. The dc current gain (0.8 kA/cm 2) decreased to 57 after 10 000 h of reliability testing. The devices showed an f T = 61 GHz and f max = 103 GHz. The reliability results are the highest ever achieved for InGaP/GaAs HBT and these results indicate the great potential of InGaP/GaAs HBT for numerous low-and high-frequency microwave circuit applications. The reliability improvements are probably due to the initial low base current at low current densities which result from the low surface recombination of InGaP and the high valence band discontinuity between InGaP and GaAs.
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Microelectronics Reliability, 1996
A field-induced degradation mechanism responsible for the surface base current drift in GaAs HBT's is studied on the basis of accelerated life-tests : two stress conditions are applied to HBT's and associated TLM structures. An EDX analysis performed on the base ohmic contact confirms the migration of metallic species which are assessed to spread into the extrinsic base region of AIGaAs/GaAs HBT's. The self-passivated GalnP/GaAs technology is expected to improve the HBT reliability.
Hydrogen induced degradation in GaInP/GaAs HBTs revealed by low frequency noise measurements
MRS Proceedings, 2004
ABSTRACTOne of today's challenges to enable the improved electrical performances and reliability of microelectronic devices consists in controlling impurities contamination: hydrogen appears to be present in most (if not all) the processes steps of the devices making (ambient atmosphere, or associated with AsH3 -VPE or AsCl3 -VPE for example in GaAs based devices,…). Hydrogen induced reliability has already been investigated for many Si or GaAs based technologies ((C)MOS, FET, HEMT, PHEMT as well as HBT devices). These effects of hydrogen on electrical behavior and on long term reliability are very difficult to understand because of the different nature and ionic association of hydrogen (H, H+, H-, H2, or associated with impurities (Ge-H, Be-H, C-H,…). Most of these studies make use of IR, SIMS, Hall measurements: in this paper, we use low frequency noise measurements, associated with static as well as dynamic characterization to identify the degradation process in GaInP/GaAs He...
Role of Neutral Base Recombination in High Gain AlGaAs/GaAs HBT’s
Neutral base recombination is a limiting factor controlling the maximum gain of AlGaAs/GaAs HBT's with base sheet resistances between 100 and 350 = : In this work, we investigate five series of AlGaAs/GaAs HBT growths in which the base thickness was varied between 500 and 1600Å and the base doping level between 2.9 2 and 4.7 2 10 19 cm 03 : The dc current gain of large area devices (L = 75 m 2 75 m) varies by as much as a factor of two at high injection levels for a fixed base sheet resistance, depending on the growth optimization. One of these series (Series TA) has the highest current gains ever reported in this base sheet resistance range, with dc current gains over 225 (@ 200 A/cm 2 ) at a base sheet resistance of 330 = : A high dc current gain of 220 (@ 10 kA/cm 2 ) was also confirmed in small area devices (L = 8 m 28 m). High-frequency tests on a separate set of wafers grown under the same conditions indicate these high current gains can be achieved without compromising the RF characteristics: Both high and normal gain devices exhibit an ft 68 GHz and fmax 100 GHz. By fitting the base current as a sum of two components, one due to recombination in the neutral base and the other in the space charge region, we conclude that an improvement in the minority carrier lifetime is responsible for the observed increase in dc current gain. Moreover, we observe a thickness-dependent variation in the effective minority carrier lifetime as the gains increase, along with a nonlinear dependence of current gain on base doping. Both phenomena are discussed in terms of an increase in Auger and radiative recombination relative to Hall-Shockley-Read recombination in optimized samples.
Recombination Investigation of InGaP HBT's
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Influence of Built-In Drift Fields on the Performance of InP-Based HBTs Grown by Solid-Source MBE
IEEE Transactions on Electron Devices, 2000
The versatility of solid-source molecular beam epitaxy for the growth of InP/InGaAs heterojunction bipolar transistors (HBTs) is provided by its excellent control of doping and composition grading profiles in combination with its efficiency for carbon doping. Various designs using doping grading or composition grading in the base are investigated to provide a built-in quasi-electric field that enhances electron transport. All graded-base devices exhibit higher current gains (β), as compared to uniform-base structures, but the β improvements are found to be nonproportional to the generated built-in drift fields. The best performances are obtained with a 9% linear composition grading profile. As compared to conventionally grown uniform-base structures, the linearly graded-base HBTs show higher current gains (up to 42%), which is of particular importance particularly in analog and mixed-signal applications.
Solid-State Electronics, 2000
AlGaAs/GaAs single HBTs from two dierent epi-layers with similar layer design, but with some variations in layer properties due to the particular features of individual epitaxial growth techniques, were simultaneously fabricated using a self-aligned process. These HBTs were tested for their reliability characteristics as well as their material quality using photo-luminescence and transmission electron microscopy. HBTs from one epi-layer showed high reliability characteristics and presented smaller carrier recombination lifetime (t B I 150 ps) in the base compared to devices from the other epi-layer (t B I 60 ps), which showed low reliability characteristics. Using XTEM images, it was found that devices with higher degree of reliability show abrupt base-emitter junction vs lowreliability devices, which appeared to have compositionally graded base-emitter hetero-interface. 7
Microelectronics Reliability, 2009
We investigated the reliability of InP-based HBTs with a ledge structure, focusing on emitter-metal-diffusion-induced degradation. Bias-temperature accelerated tests under high temperatures and high current densities of up to 5 mA/lm 2 were conducted for HBTs with conventional emitter electrodes, whose metal configuration was Ti/Pt/Au, and for HBTs with refractory metal emitters of Ti/Mo-Ti/Pt/ Au, Ti/W-Ti/Pt/Au, or W-Ti/Pt/Au. The emitter contact layer was analyzed by transmission electron microscopy, energy dispersive X-ray spectroscopy, and transmission electron diffraction. Severe damage and disruption of uniformity of the atomic composition were observed due to diffusion of Ti and Au in HBTs with conventional emitter, whereas suppression of those degradations was observed in HBTs with refractory emitter. Refractory metals were found to be advantageous for blocking upper metal diffusion. Interstitials of host species generated due to metal diffusion must cause a shift of atomic composition. The time-wise change in the emitter resistance was estimated to compare the speed of the contact layer degradation between different emitter electrode metals. The critical time, which we determined as an emitter resistance increases of 3% from the initial value, increased by one order for HBTs with refractory metal than for HBTs with conventional metal at the same junction temperature, despite the same activation energy of 2.0 and 1.65 eV for J c of 2 and 5 mA/lm 2 , respectively, for all types of emitter electrode. The advantages of refractory metal for improving the reliability of InP HBTs were confirmed, especially for operation at high current densities.
Highly reliable InP-based HBTs with a ledge structure operating at high current density
Electronics and Communications in Japan (Part II: Electronics), 2007
For the InP HBT being developed for 40 Gbit/s optical communication system realization, the effectiveness of the ledge structure for enhancement of device lifetime due to suppressing generation of the surface recombination current is confirmed. An accelerated life test for this structure shows that the activation energy of the mode in which the current gain decreases gradually is 1.7 eV, that the device life extrapolated at 125 °C is more than 1 × 10 8 hours, and that this degradation does not depend on the operating current density up to 2 mA/µm 2. Thus, high reliability at a high current density allowing high-speed design is realized. Also, the degradation mechanism of the current gain is analyzed. It is found that sudden degradation can be controlled by increasing the layer thickness of the emitter and can consequently be eliminated. The above results confirm that the authors' InP HBT has sufficient reliability for practical implementation.