Difference between revisions of "Hybrid Silicon Process Overview"

Revision as of 09:23, 19 October 2012

Summary

The hybrid silicon process can be summarized as follows:
(1) Silicon-layer processing
Starting with an SOI (Silicon on Insulator) wafer, rib waveguides are patterned in the top silicon and vertical channels are etched to the buried oxide (the purpose of these vertical channels is to allow outgasing during bonding steps later in the process). Additional steps to introduce diodes into the silicon through doping are also possible, as are additional etch steps for gratings.
(2) III-V bonding and processing
III-V epi material is then die-bonded to the silicon and back-polished until a thin stack of III-V remains, after which wet etching removes the remainder of excess Indium Phosphide (there is typically a p-contact layer of InGaAs beneath this which acts as an etch stop). Gain elements are then patterned in the III-V by etching down through the epi stack roughly to the quantum wells (this patterned stack is then referred to as the "mesa"), a second etch step goes through the quantum wells to the n-InP, and finally the n-InP can be etched until the underlying silicon is exposed.
(3) Metallization
Thick p-contact metal is deposited on top of the mesa (although thin metal may already have been deposited for this purpose during the mesa definition). The mesa is then typically either subjected to a proton implantation step or an etch step to confine current to a narrow path directly beneath the p-contact. Metal for n-contacts is deposited, and a "buffer" layer (SU8, BCB, oxide, or some other dielectric) is added to allow metal traces to be overlaid on top of the waveguides without impacting the optical mode. Vias are etched through the buffer and "probe" metal (i.e. thick metal for probing and wirebonding) is deposited on top and patterned.

The actual process used to accomplish these steps is dependent on the project; in many of these steps there are a range of options available for processing. Below is a core process which should be considered the "template"; additional modules can be added to this as desired - these are provided below the core process along with a description of what they provide and their current status.

Core process

This is the core process which should be considered the "template"; additional modules can be added to this as desired.

Core Process Outline

Optional process modules

These are process "modules" which can be selected as needed and added to the Core process (in some cases as alternatives to core process steps).
The established maturity (and therefore yield) of each module varies; add modules to suit individual applications, but be aware that each deviation from the core process introduces additional risk.