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MonolithIC 3D Inc. , Patents Pending
MonolithIC 3D ICs
October 2012
1MonolithIC 3D Inc. , Patents Pending
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Chapter 1Monolithic 3D
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 electro-optic 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 on-chip 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
TSV diameter typically ~5um Limited by alignment accuracy and silicon thickness
Processed Top Wafer
Processed Bottom Wafer
Align and bond
TSVTSV
Figure 1
Two Types of 3D Technology
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3D-TSVTransistors made on separate wafers @ high temp., then thin + align + bond
TSV pitch > 1um*
Monolithic 3DTransistors made monolithically atop
wiring (@ sub-400oC for logic)
TSV pitch ~ 50-100nm
10um-50um 100
nm
* [Reference: P. Franzon: Tutorial at IEEE 3D-IC Conference 2011]
Figure 2ITRS Roadmap compared to monolithic 3D
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TSV (parallel) vs. Monolithic (sequential)
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Source: CEA Leti Semicon West 2012 presentation
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 transferSee 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).
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*Soitec’s fundamental patent US 5,374,564 expired Sep. 15, 2012
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 3Using ion-cutting to place a thin layer of monocrystalline silicon
above a processed (transistors and metallization) base wafer
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p- Si
Oxide
p- Si
OxideH
Top layer
Bottom layer
Oxide
Hydrogen implant
of top layerFlip top layer and
bond to bottom layer
Oxide
p- Si
Oxide
H
Cleave using <400oC
anneal or sideways
mechanical force.
CMP.
OxideOxide
Similar process (bulk-to-bulk) used for manufacturing all SOI wafers today
p- Si
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Chapter 2Monolithic 3D RCAT
MonolithIC 3D – The RCAT path
The Recessed Channel Array Transistor (RCAT) fits very nicely into the hot-cold process flow partitionRCAT is the transistor used in commercial DRAM as its 3D channel overcomes the short channel effect
Used in DRAM production @ 90nm, 60nm, 50nm nodesHigher 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
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Wafer, ~700µm
~100nm
P-
N+P-
Using a new wafer, construct dopant regions in top ~100nm and activate at ~1000º C
Oxide
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~100nm
P-
N+P-
Oxide
Implant Hydrogen for Ion-Cut
H+
Wafer, ~700µm
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~100nm
P-
N+P-
~10nm H+
Oxide
Hydrogen cleave plane for Ion-Cut formed in donor wafer
Wafer, ~700µm
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~100nm N+P-
Oxide
1µ Top Portion ofBase Wafer
H+
Flip over and bond the donor wafer to the base (acceptor) wafer
Base Wafer, ~700µm
Donor Wafer, ~700µm
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~100nm N+P-
Oxide
1µ Top Portion ofBase Wafer
Perform Ion-Cut Cleave
Base Wafer ~700µm
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~100nm N+P-
Oxide
1µ Top Portion ofBase Wafer
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Complete Ion-Cut
Base Wafer ~700µm
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~100nm N+P-
Oxide
1µ Top Portion ofBase Wafer
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Etch Isolation regions as the first step to define RCAT transistors
Base Wafer ~700µm
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~100nm N+P-
Oxide
1µ Top Portion ofBase Wafer
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Fill isolation regions (STI-Shallow Trench Isolation) with Oxide, and CMP
Base Wafer ~700µm
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~100nm N+P-
Oxide
1µ Top Portion ofBase Wafer
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Etch RCAT Gate Regions
Base Wafer ~700µm
Gate region
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~100nm N+P-
Oxide
1µ Top Portion ofBase Wafer
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Form Gate Oxide
Base Wafer ~700µm
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~100nm N+P-
Oxide
1µ Top Portion ofBase Wafer
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Form Gate Electrode
Base Wafer ~700µm
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~100nm N+P-
Oxide
1µ Top Portion ofBase Wafer
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Add Dielectric and CMP
Base Wafer ~700µm
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~100nm N+P-
Oxide
1µ Top Portion ofBase Wafer
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Etch Thru-Layer-Via and RCAT Transistor Contacts
Base Wafer ~700µm
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~100nm N+P-
Oxide
1µ Top Portion ofBase Wafer
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Fill in Copper
Base Wafer ~700µm
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~100nm N+P-
Oxide1µ Top Portion of
Base (acceptor) Wafer
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Add more layers monolithically
Base Wafer ~700µm
Oxide
~100nm N+P-
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Chapter 3Monolithic 3D HKMG
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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.
Technology
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~700µm Donor Wafer
On the donor wafer, fabricate standard dummy gates with oxide and poly-Si; >900ºC OK
PMOSNMOS
Silicon
PolyOxide
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~700µm Donor Wafer
Form transistor source/drain
PMOSNMOS
Silicon
PolyOxide
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~700µm Donor Wafer
PMOSNMOS
Silicon
Form inter layer dielectric (ILD), S/D implants and high temp anneals, CMP to transistor tops
CMP to top of dummy gatesILDS/D Implant
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~700µm Donor Wafer
PMOSNMOS
Silicon
Implant hydrogen to generate cleave plane
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~700µm Donor Wafer
PMOSNMOS
Silicon
Implant hydrogen to generate cleave plane
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~700µm Donor Wafer
PMOSNMOS
Silicon
Implant hydrogen to generate cleave plane
H+
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~700µm Donor Wafer
Silicon
Bond donor wafer to carrier wafer
H+
~700µm Carrier Wafer
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~700µm Donor Wafer
Cleave to remove bulk of donor wafer
H+
~700µm Carrier Wafer
Transferred Donor Layer
Silicon
Silicon
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CMP to STI
~700µm Carrier Wafer
STITransferred
Donor Layer
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Deposit oxide, ox-ox bond carrier structure to base wafer that has transistors & circuits
~700µm Carrier Wafer
STI
Oxide-oxide bond
PMOSNMOS
Transferred Donor Layer
Base Wafer
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Remove carrier wafer
Oxide-oxide bond
~700µm Carrier Wafer
Transferred Donor Layer
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PMOSNMOSBase Wafer
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Carrier wafer had been removed
Oxide-oxide bond
Transferred Donor Layer
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PMOSNMOSBase Wafer
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Replace dummy gate stacks with Hafnium Oxide & metal at low temp
Oxide-oxide bond
Transferred Donor Layer
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PMOSNMOSBase Wafer
Note: Replacing oxide and gate result in oxide and gate that were not damaged by the H+ implant
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Form inter layer via through oxide only (similar to standard via)
Oxide-oxide bond
Transferred Donor Layer
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PMOSNMOSBase Wafer
Note: The second mono-crystal layer is very thin (<100nm) and via through it, is similar to other vias in the metal stack
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Form top layer interconnect and connect layers with inter layer via
Oxide-oxide bond
Transferred Donor Layer
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PMOSNMOSBase Wafer
ILV
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• 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
Benefits for RCAT and HKMG