Controllable, low damage dry etching of heterojunction bipolar transistors and horizontal distributed Bragg reflector mirrors using an electron cyclotron resonance source.

Low damage, controllable dry etching of a variety of III-V materials is developed. The materials include GaInAs and AlInAs for fabrication of heterojunction bipolar transistors (HBTs), and GaAs and InP for horizontal distributed Bragg reflectors (HDBRs) and via holes. Etch characteristics including etch rate, sidewall profile, surface morphology, and etch induced damage must be controlled and readily modified for varying device requirements. Plasma etching is used to provide a directional component to the etch, but surface damage results from the bombardment of energetic ions needed for practical etch rates and profile control. To simultaneously meet the needs of profile control, high etch rates, and low damage, an electron cyclotron resonance source has been used. Electrical damage to GaInAs resulting from exposure to a Cl$\sb2$/Ar plasma has been studied using transmission lines. The specific contact resistivity $\rm(\rho\sb{c})$ of Ti/Pt/Au on GaInAs was found to be more sensitive to surface damage than were Schottky diode characteristics. Defects generated by dry etching caused a reduction in $\rm\rho\sb{c}$ for n-GaInAs and an increase in $\rm\rho\sb{c}$ for p-GaInAs. The damage depth was $\le$6 nm at 50 W rf power and increased to $\sim$18 nm at 200 W rf power. Minimal surface damage was obtained when low rf power was used. After annealing, $\rm\rho\sb{c}$ for the p-GaInAs base layer was lower for optimized dry etching conditions compared to wet etching. This is due to the smoother surface morphology obtained after dry etching as measured by atomic force microscopy. The endpoint for HBT emitter etching was determined using optical emission spectroscopy (OES). Optical emission from atomic In at 410.2 nm and Ga at 417.2 nm have been detected with the strongest signal to background ratio. For abrupt junctions, $<$3 nm of the GaInAs base material is removed. For junctions with superlattice layers, endpoint can be obtained within 6 nm of the p$\sp+$ base region. Mass spectrometry has also been used to monitor P and As etch products. These signals have been studied for varying etch conditions and have been correlated to the etch rates. The ability of the mass spectrometer to detect the group V etch products coupled with the ability of OES to detect the group III elements allows for non-invasive real-time control of a variety of III-V material systems. The wafer temperature has been studied by using in situ fiberoptic thermometry which provides a direct measure of the wafer surface. A new device structure is proposed which allows the demonstration of high aspect ratio, high etch rate and selectivity, and low damage etching. The device is an HDBR Fabry-Perot interferometer, which consists of alternating layers of semiconductor and air. A highly anisotropic etch was developed to define plates 122 nm wide in InP and 59 nm wide in GaAs.PhDApplied SciencesElectrical engineeringMaterials scienceUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/130628/2/9732222.pd