Bonding method
Ni-Si bonding
Ni-InGaAs bonding
Schematic
Description
Bonding with multiple dielectric stack layers:
 HfO2 is used for HF resist layer (10 nm)
 Al2O3 acts as block layer for F-etch (6 nm)
 SiO2 prevents electronic leakage (200 nm)
 Ni is used for Nickel Silicide bonding (Ti 25 nm, Ni
100 nm)
Bonding with nothing beneath InGaAs window:
 No need to remove SiNx layer
 The broken window provides natural hollow square
for Ni film evaporation
 Ni for Ni-InGaAs bonding (Ti 5 nm, Ni 20 nm)
1. Ni deposition on SiNx/Si TEM grid
2. Bonding at 350’C; Before lapping and HCl etching, grow
a think layer (300 nm) SiO2 from the backside, to support
the InGaAs suspended film
st
3. Write global/chip marks, and location numbers in the 1 EBL step, followed by evaporation of Ni/Au/Ni
1. Multiple layers (Ni/SiO2/Al2O3/HfO2) deposition on
InGaAs/InP substrate
2. Bonding at 400’C, followed by lapping and HCl etching
Processing Flow
4. Write Ni Lines in the 2nd EBL step, which are used as support for InGaAs membrane as well as the source for alloy
reaction.
5. Write Fin structures in the 3rd EBL step, with various orientations, both to compensate the rotation of sample alignment
and to study their diffusion behaviors.
Notes
 The multiple layers underneath InGaAs window can be
 This process avoids complex stacking of dialectic layers
removed by HNO3 (for Ni), and F-etch (for SiO2)
 The post-grown SiO2 from the backside can later be
 HfO2 thickness has been decreased to 10nm,
removed by HF dip
compensated by another 6nm Al2O3 for supporting
1. I tried two method for HCl etching:
1. The window was always broken during the HCl etching:
(1) The lapped sample was not released from the holding wafer
during etching, and the bonded sample was previously mounted by
large droplet of PMMA C2.
(1) In the first attempt, I used Ti 7nm/Ni 25 nm for the bonding,
which survives the lapping but not the HCl etch.
Current Problems
In this bonded sample, the window looks uniform, but we are not
sure whether it’s flat or convex/concave. It was broken after spin
The surface was rough after HCl etch, and the center seemed
attacked by HCl, leaving no suspended InGaAs film.
I thought the reason might be that the 25nm has fully reacted
coating and 170’C bake.
(2) The lapped sample was released from the holding wafer before
HCl etch, and the bonded sample was previously mounted by wax.
through the InGaAs layer and the Ni-InGaAs alloy was also slowly
etched in HCl solution. So, I changed the thickness of metal layer to
5nm Ti/ 20nm Ni.
(2) In the seconded attempt, thinner Ti/Ni was used.
Longer time etch
The film was unbroken, but the wrinkles can be found at the
window, which might be due to the build-in stress. (from Ni-Si
reaction? From introduced new Al2O3 layer?)
Shorter time etch
The surface become relatively smoother compared with last time,
but both windows of the two samples this time are broken. Worried
about the over-etch problem, so I decrease the etching time.
However, even though the InP was not fully removed, the window
has already broken and the edges of window seem to be attacked by
etching.
Any way to avoid this?
Previously, I tried the patterned bonding for self-aligned S/D, some
places of the unreacted area will break while others are not. There
seem some changes of break the suspended film. Shall we go with
TEM grids with multiple small windows?