Optimized emitter-base interface cleaning for advanced Heterojunction Bipolar Transistors
Résumé
A B S T R A C T
Heterojunction Bipolar Transistors needed for high-frequency applications require precise dopant control. Insitu doped epitaxies used during device fabrication rely on surface preparation to obtain an optimized doping
profile. Defects due to imperfect cleaning relates to high emitter resistance and low-frequency noise.
Base epitaxy is followed by the fabrication of thin L-shaped oxide spacers and in-situ arsenic-doped emitter
epitaxy by Low Pressure Chemical Vapor Deposition. A cleaning step between spacers formation and emitter
epitaxy is mandatory to remove residual contamination. Hydrofluoric acid (HF) wet cleaning, in-situ remote
plasma cleaning (SiconiTM) and thermal treatments have been tested. A minimum etching budget is sought for
limiting spacer consumption while adequately cleaning the interface.
Time Of Flight-Secondary Ion Mass Spectroscopy (TOF-SIMS) and High-Resolution Transmission Electron
Microscopy (HR-TEM) are used to characterize the interface and measure levels of arsenic, oxygen, fluorine
and carbon. Emitter resistance and base-emitter breakdown voltage measurements are used to show the impact
on electrical figures of merit. Siconi targeting 10 Å of thermal oxide removal followed by a thermal treatment
(800 ◦C, 60 s) in the deposition chamber results the best process among the tested ones.