Hydrogen induced degradation in GaInP/GaAs HBTs revealed by low frequency noise measurements

One 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 technologies Si or GaAs based ((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 Heterojunction Bipolar Devices (HBT provided by Thomson LCR). Firstable, we will present the influence of passivation (SiN and GaInP ledge) on the reliability associated with Hydrogen : low frequency noise measurements will be performed in the range of 250Hz to 100 kHz. The noise spectra evolutions (current and voltage noise sources at the input of the device, and their correlation) will allow us to identify the activation process responsible of the static and dynamic rise and fall of the HBT’s current gain. C-H complexes have been proved to be the process responsible of this degradation. Additive reliability tests have been performed on two sets of devices (featuring different emitter length) under two distinct stocking conditions (temperature and biasing of the devices) leading to different junctions temperatures : low frequency and high frequency noise measurements, associated with static and dynamic S parameters measurements will lead to the same conclusions about the hydrogen chemical reaction. C-H complexes breaking, and diffusion of H towards the extrinsic surface of the device have been observed. Sealed devices have proved to get the same degradation signature than on wafer devices : Hydrogen is assumed to be present in high concentration levels in the device layers, and reacts under thermal and electrical stress. This study will also present the emitter orientation effects on the reliability, i.e. of the piezoelectric contribution both to electrical performances and reliability level of the device.