MonolithIC 3D ICs
October 2012
MonolithIC 3D Inc. , Patents Pending
MonolithIC 3D Inc. , Patents Pending
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Chapter 1
Monolithic 3D
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3D ICs at a glance
A 3D Integrated Circuit is a chip that has active
electronic components stacked on one or more layers
that are integrated both vertically and horizontally
forming a single circuit.
Manufacturing technologies:
-Monolithic
-TSV based stacking
-Chip Stacking w/wire bonding
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MonolithIC 3D
A technology breakthrough allows the fabrication of
semiconductor devices with multiple thin tiers (<1um) of copper
connected active devices utilizing conventional fab equipment.
MonolithIC 3D Inc. offers solutions for logic, memory and electrooptic technologies, with significant benefits for cost, power and
operating speed.
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Comparison of Through-Silicon Via (TSV) 3D
Technology and Monolithic 3D Technology
The semiconductor industry is actively pursuing 3D Integrated Circuits
(3D-ICs) with Through-Silicon Via (TSV) technology (Figure 1). This can also
be called a parallel 3D process.
As shown in Figure 2, the International Technology Roadmap for
Semiconductors (ITRS) projects TSV pitch remaining in the range of several
microns, while on-chip interconnect pitch is in the range of 100nm.
The TSV pitch will not reduce appreciably in the future due to bonder
alignment limitations (0.5-1um) and stacked silicon layer thickness (6-10um).
While the micron-ranged TSV pitches may provide enough vertical
connections for stacking memory atop processors and memory-on-memory
stacking, they may not be enough to significantly mitigate the well-known onchip interconnect problems.
Monolithic 3D-ICs offer through-silicon connections with <50nm
diameter and therefore provide 10,000 times the areal density of TSV
technology.
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Typical TSV process
Processed
Top Wafer
Figure 1
TSV
TSV
Align and bond
Processed
Bottom
Wafer

 TSV diameter typically ~5um
Limited by alignment accuracy and silicon thickness
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Two Types of 3D Technology
3D-TSV
Monolithic 3D
Transistors made on separate wafers
@ high temp., then thin + align + bond
Transistors made monolithically atop
wiring (@ sub-400oC for logic)
10um50um
100
nm
TSV pitch > 1um*
TSV pitch ~ 50-100nm
* [Reference: P. Franzon: Tutorial at IEEE 3D-IC Conference 2011]
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Figure 2
ITRS Roadmap compared to monolithic 3D
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TSV (parallel) vs. Monolithic (sequential)
Source: CEA Leti Semicon West 2012 presentation
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The Monolithic 3D Challenge
 Once copper or aluminum is added on for bottom
layer interconnect, the process temperatures need to
be limited to less than 400ºC !!!
 Forming single crystal silicon requires ~1,200ºC
 Forming transistors in single crystal silicon requires ~800ºC
 The TSV solution overcame the temperature challenge by
forming the second tier transistors on an independent wafer,
then thinning and bonding it over the bottom wafer (‘parallel’)
The limitations:
 Wafer to wafer misalignment ~ 1µ
 Overlaying wafer could not be thinned to less than 50µ
The Monolithic 3D Innovation

Utilize Ion-Cut (‘Smart-Cut’) to transfer a thin (<100nm) single
crystal layer on top of the bottom (base) wafer
 Form the cut at less than 400ºC *
 Use co-implant
 Use mechanically assisted cleaving
 Form the bonding at less than 400ºC *
* See details at: Low Temperature Cleaving, Low Temperature Wafer
Direct Bonding

Split the transistor processing to two portions
 High temperature process portion (ion implant and activation) to be
done before the Ion-Cut
 Low temperature (<400°C) process portion (etch and deposition) to be
done after layer transfer
See details in the following slides:
Monolithic 3D ICs
Using SmartCut technology - the ion cutting process that
Soitec uses to make SOI wafers for AMD and IBM (millions of
wafers had utilized the process over the last 20 years) - to stack
up consecutive layers of active silicon (bond first and then cut).
Soitec’s Smart Cut Patented* Flow (follow this link for video).
*Soitec’s fundamental patent US 5,374,564 expired Sep. 15, 2012
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Monolithic 3D ICs
Ion cutting: the key idea is that if you implant a thin layer
of H+ ions into a single crystal of silicon, the ions will weaken the
bonds between the neighboring silicon atoms, creating a fracture
plane (Figure 3). Judicious force will then precisely break the
wafer at the plane of the H+ implant, allowing you to in-effect
peel off very thin layer. This technique is currently being used to
produce the most advanced transistors (Fully Depleted SOI,
UTBB transistors – Ultra Thin Body and BOX), forming
monocrystalline silicon layers that are less than 10nm thick.
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Figure 3
Using ion-cutting to place a thin layer of monocrystalline silicon
above a processed (transistors and metallization) base wafer
Cleave using <400oC
Hydrogen implant
Oxide
anneal or sideways
Flip top layer and
of top layer
mechanical force. CMP.
bond to bottom layer
p- Si
Top layer
Oxide
p- Si
Oxide
H
p- Si
H
Oxide
Oxide
p- Si
Oxide
Oxide
Bottom layer
Similar process (bulk-to-bulk) used for manufacturing all SOI wafers today
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Chapter 2
Monolithic 3D RCAT
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MonolithIC 3D – The RCAT path
The Recessed Channel Array Transistor (RCAT) fits very
nicely into the hot-cold process flow partition
RCAT is the transistor used in commercial DRAM as its 3D
channel overcomes the short channel effect
Used in DRAM production @ 90nm, 60nm, 50nm nodes
Higher capacitance, but less leakage, same drive current
The following slides present the flow to process an RCAT
without exceeding the 400ºC temperature limit
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RCAT – a monolithic process flow
Using a new wafer, construct dopant regions in top ~100nm
and activate at ~1000ºC
Oxide
~100nm
Wafer, ~700µm
PN+
P-
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Implant Hydrogen for Ion-Cut
H+
Oxide
P~100nm
N+
Wafer, ~700µm
P-
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Hydrogen cleave plane
for Ion-Cut formed in donor wafer
Oxide
P~100nm
N+
Wafer, ~700µm
H+
~10nm
P-
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Flip over and bond
the donor wafer to the base (acceptor) wafer
Donor Wafer,
~700µm
N+
POxide
H+
~100nm
1µ Top Portion of
Base Wafer
Base Wafer,
~700µm
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Perform Ion-Cut Cleave
~100nm
N+
POxide
1µ Top Portion of
Base Wafer
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Base Wafer
~700µm
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Complete Ion-Cut
~100nm
N+
POxide
1µ Top Portion of
Base Wafer
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Base Wafer
~700µm
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Etch Isolation regions as the first step to define
RCAT transistors
~100nm
N+
POxide
1µ Top Portion of
Base Wafer
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Base Wafer
~700µm
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Fill isolation regions (STI-Shallow Trench
Isolation) with Oxide, and CMP
~100nm
N+
P-
Oxide
1µ Top Portion of
Base Wafer
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Base Wafer
~700µm
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Etch RCAT Gate Regions
Gate region
~100nm
N+
P-
Oxide
1µ Top Portion of
Base Wafer
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Base Wafer
~700µm
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Form Gate Oxide
~100nm
N+
P-
Oxide
1µ Top Portion of
Base Wafer
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Base Wafer
~700µm
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Form Gate Electrode
~100nm
N+
POxide
1µ Top Portion of
Base Wafer
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Base Wafer
~700µm
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Add Dielectric and CMP
~100nm
N+
POxide
1µ Top Portion of
Base Wafer
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Base Wafer
~700µm
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Etch Thru-Layer-Via and
RCAT Transistor Contacts
~100nm
N+
POxide
1µ Top Portion of
Base Wafer
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Base Wafer
~700µm
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Fill in Copper
~100nm
N+
P-
Oxide
1µ Top Portion of
Base Wafer
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Base Wafer
~700µm
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Add more layers monolithically
~100nm
~100nm
N+
P-
Oxide
N+
P-
Oxide
1µ Top Portion of
Base (acceptor) Wafer
Base Wafer
~700µm
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Chapter 3
Monolithic 3D HKMG
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Technology
The monolithic 3D IC technology is applied to produce
monolithically stacked high performance High-k Metal Gate
(HKMG) devices, the world’s most advanced production
transistors.
3D Monolithic State-of-the-Art transistors are formed with ion-cut
applied to a gate-last process, combined with a low
temperature face-up layer transfer, repeating layouts, and an
innovative
inter-layer
via
(ILV)
alignment
scheme.
Monolithic 3D IC provides a path to reduce logic, SOC, and
memory costs without investing in expensive scaling down.
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On the donor wafer, fabricate standard dummy
gates with oxide and poly-Si; >900ºC OK
NMOS
Poly
Oxide
PMOS
~700µm Donor Wafer
Silicon
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Form transistor source/drain
NMOS
Poly
Oxide
PMOS
~700µm Donor Wafer
Silicon
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Form inter layer dielectric (ILD), do high temp
anneals, CMP near to transistor tops
S/D Implant
NMOS
ILD
PMOS
CMP near to
top of dummy
gates
~700µm Donor Wafer
Silicon
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Implant hydrogen to generate cleave plane
NMOS
PMOS
~700µm Donor Wafer
Silicon
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Implant hydrogen to generate cleave plane
NMOS
PMOS
~700µm Donor Wafer
Silicon
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Implant hydrogen to generate cleave plane
NMOS
PMOS
H+
~700µm Donor Wafer
Silicon
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Bond donor wafer to carrier wafer
~700µm Carrier Wafer
H+
~700µm Donor Wafer
Silicon
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Cleave to remove bulk of donor wafer
~700µm Carrier Wafer
Transferred
Donor Layer
(nm scale)
Silicon
H+
~700µm Donor Wafer
Silicon
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CMP to STI
~700µm
Carrier Wafer
Transferred
Donor Layer
(<100nm)
STI
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Deposit oxide, ox-ox bond carrier structure to
base wafer that has transistors & circuits
~700µm
Carrier Wafer
Transferred
Donor Layer
(<100nm)
STI
Oxide-oxide bond
~700µm
Base Wafer
NMOS
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PMOS
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Remove carrier wafer
~700µm
Carrier Wafer
Transferred
Donor Layer
(<100nm)
Oxide-oxide bond
~700µm
Base Wafer
NMOS
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PMOS
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Carrier wafer had been removed
Transferred
Donor Layer
(<100nm)
Oxide-oxide bond
~700µm
Base Wafer
NMOS
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PMOS
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CMP to expose gate stacks. Replace dummy gate
stacks with Hafnium Oxide & Metal (HKMG)at low temp
Note: Replacing the gate oxide and gate electrode results in a gate stack that is not damaged
by the H+ implant
Transferred
Donor Layer
(<100nm)
Oxide-oxide bond
~700µm
Base Wafer
NMOS
PMOS
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Form inter layer via (ILV) through oxide only
(similar to standard via)
Note: The second mono-crystal layer is very thin (<100nm) and has a vertical oxide corridor; hence, the
via through it (TLV) may be constructed and sized similarly to other vias in the normal metal stack.
Transferred
Donor Layer
(<100nm)
Oxide-oxide bond
~700µm
Base Wafer
NMOS
PMOS
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Form top layer interconnect and
connect layers with inter layer via
ILV
Transferred
Donor Layer
(<100nm)
Oxide-oxide bond
~700µm
Base Wafer
NMOS
PMOS
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Benefits for RCAT and HKMG
• Maximum State-of-the-Art transistor performance on
multi-strata
• 2x lower power
• 2x smaller silicon area
• 4x smaller footprint
• Performance of single crystal silicon transistors on all
layers in the 3DIC
• Scalable: scales normally with equipment capability
• Forestalls next gen litho-tool risk
• High density of vertical interconnects enable innovative
architectures, repair, and redundancy
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Chapter 4
Monolithic 3D RC-JLT
(Recessed-Channel Junction-Less Transistor)
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Technology
Monolithic 3D IC technology is applied to producing monolithically stacked low
leakage Recessed Channel Junction-Less Transistors (RC-JLTs).
Junction-less (gated resistor) transistors are very simple to manufacture, and
they scale easily to devices below 20nm:
•
Bulk Device, not surface
•
Fully Depleted channel
•
Simple alternative to FinFET
Superior contact resistance is achieved with the heavier doped top layer. The
RCAT style transistor structure provides ultra-low leakage.
Monolithic 3D IC provides a path to reduce logic, SOC, and memory costs
without investing in expensive scaling down.
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RCJLT – a monolithic process flow
Using a new wafer, construct dopant regions in top ~100nm
and activate at ~1000ºC
Oxide
~100nm
Wafer, ~700µm
N+
N++
P-
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Implant Hydrogen for Ion-Cut
H+
Oxide
~100nm N+
N++
Wafer, ~700µm
P-
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Hydrogen cleave plane
for Ion-Cut formed in donor wafer
Oxide
N+
~100nm
N++
Wafer, ~700µm
H+
~10nm
P-
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Flip over and bond
the donor wafer to the base (acceptor) wafer
Donor Wafer,
~700µm
P-
~100nm N++
N+
Oxide
H+
1µ Top Portion of
Base Wafer
Base Wafer,
~700µm
MonolithIC 3D Inc. Patents Pending
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Perform Ion-Cut Cleave
N++
~100nm N+
Oxide
1µ Top Portion of
Base Wafer
MonolithIC 3D Inc. Patents Pending
Base Wafer
~700µm
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Complete Ion-Cut
~100nm
N++
N+
Oxide
1µ Top Portion of
Base Wafer
MonolithIC 3D Inc. Patents Pending
Base Wafer
~700µm
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Etch Isolation regions as the first step to define
RCAT transistors
~100nm
N++
N+
Oxide
1µ Top Portion of
Base Wafer
MonolithIC 3D Inc. Patents Pending
Base Wafer
~700µm
58
Fill isolation regions (STI-Shallow Trench
Isolation) with Oxide, and CMP
~100nm N++
N+
Oxide
1µ Top Portion of
Base Wafer
MonolithIC 3D Inc. Patents Pending
Base Wafer
~700µm
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Etch RCAT Gate Regions
Gate region
~100nm
N++
N+
Oxide
1µ Top Portion of
Base Wafer
MonolithIC 3D Inc. Patents Pending
Base Wafer
~700µm
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Form Gate Oxide
~100nm
N++
N+
Oxide
1µ Top Portion of
Base Wafer
MonolithIC 3D Inc. Patents Pending
Base Wafer
~700µm
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Form Gate Electrode
~100nm
N++
N+
Oxide
1µ Top Portion of
Base Wafer
MonolithIC 3D Inc. Patents Pending
Base Wafer
~700µm
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Add Dielectric and CMP
~100nm
N++
N+
Oxide
1µ Top Portion of
Base Wafer
MonolithIC 3D Inc. Patents Pending
Base Wafer
~700µm
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Etch Thru-Layer-Via and
RCJLT Transistor Contacts
~100nm
N++
N+
Oxide
1µ Top Portion of
Base Wafer
MonolithIC 3D Inc. Patents Pending
Base Wafer
~700µm
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Fill in Copper
~100nm
N++
N+
Oxide
1µ Top Portion of
Base Wafer
MonolithIC 3D Inc. Patents Pending
Base Wafer
~700µm
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Add more layers monolithically
~100nm
~100nm
N++
N+
Oxide
N++
N+
Oxide
1µ Top Portion of
Base (acceptor) Wafer
Base Wafer
~700µm
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Benefits for RCJLT
• 2x lower power
• 2x smaller silicon area
• 4x smaller footprint
• Layer to layer interconnect density at close to full lithographic resolution
and alignment
• Performance of single crystal silicon transistors on all layers in the 3D IC
• Scalable: scales naturally with equipment capability
• Forestalls next gen litho-tool risk
• Also useful as Anti-Fuse FPGA programming transistors: programmable
interconnect is 10x-50x smaller & lower power than SRAM FPGA
• Base logic circuits could be UT-BBOX, FinFET, or JLT CMOS logic devices
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RC-JLT flow: Summary
Create a layer of Recessed Channel Junction-Less Transistors (RC-JLTs), a
junction-less version of the RCAT used in DRAMs, by activating dopants at
~1000°C before wafer bonding to the CMOS substrate and cleaving, thereby
leaving a very thin doped stack layer from which transistors are completed,
utilizing less than 400°C etch and deposition processes.
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