Abstract
An arsenic doping technique for depositing up to 40-μm-thick high-resistivity layers is presented for fabricating diodes with low RC constants that can be integrated in closely-packed configurations. The doping of the as-grown epi-layers is controlled down to 5 × 1011 cm−3, a value that is solely limited by the cleanness of the epitaxial reactor chamber. To ensure such a low doping concentration, first an As-doped Si seed layer is grown with a concentration of 1016 to 1017 cm−3, after which the dopant gas arsine is turned off and a thick lightly-doped epi-layer is deposited. The final doping in the thick epi-layer relies on the segregation and incorporation of As from the seed layer, and it also depends on the final thickness of the layer, and the exact growth cycles. The obtained epi-layers exhibit a low density of stacking faults, an over-the-wafer doping uniformity of 3.6%, and a lifetime of generated carriers of more than 2.5 ms. Furthermore, the implementation of a segmented photodiode electron detector is demonstrated, featuring a 30 pF capacitance and a 90 Ω series resistance for a 7.6 mm2 anode area.
Highlights
Recent advances in silicon photodiodes have yielded detectors with near-theoretical detection efficiencies and fast response times [1,2,3]
Since the growth rate is around 1 μm/min, and layers as thick as 40 μm are grown, we can assume that the up-diffusion of As from the seed layer can be up to 10 μm when the growth temperature of 1,050 °C and the bake steps at 1,100 °C are taken into account
The seed layer formation is followed by a desorption step at 1,100 °C to remove the As atoms that have segregated on the surface
Summary
Recent advances in silicon photodiodes have yielded detectors with near-theoretical detection efficiencies and fast response times [1,2,3]. The lateral spread of the depletion is about the same size as the thickness of the wafer which is usually greater than ~250 μm This means that for multi-segment detectors the individual photodiodes should be electrically isolated by a distance that is much greater than this. Modern solid-state detectors demand flexible multi-segmentation (pixelization) of the photosensitive surface with closely-packed segments [5] This implies that their depletion region has to be vertically wide to obtain the low capacitance and series resistance, but laterally limited in order for neighboring detector segments (adjacent diodes) to function independently. As a drawback the dark current is increased to a level that is unacceptable for many applications such as the low-energy electron detectors that have motivated the work presented in this paper These detectors were developed for use in advanced Scanning Electron Microscope (SEM) systems. A technique is developed for a controlled segregation, removal and auto-doping of As to obtain the required very lowly-doped profiles
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
