2001 ITRS Front End Process July 18, 2001 San Francisco, CA
FEP Chapter Scope • The scope of the FEP Chapter of the ITRS is to define comprehensive future requirements and identify potential solutions for the key technology areas in front-end-of-line IC wafer fabrication processing
FEP Chapter Topics • Starting Substrate Materials • Surface Preparation • Critical Dimension Etch • MOSFET Isolation, Gate Stack, Doping, and Contact Requirements • High Performance Logic • Low Operating Power Logic (new 2001 addition) • Low Standby Power Logic (new 2001 addition) • DRAM Trench and Stack Capacitor materials and processes
FEP Chapter Topics • Pre-Metal dielectric layers (new) • FLASH memory materials and processes (new) • FeRAM materials and processes (new) • Non-classical double gate CMOS materials and processes (new)
1999 vs 2001 ITRS Technology Nodes 45 nm gate length was forecasted for year 2008 in 1999 ITRS 32 nm gate length was forecasted for year 2011 in 1999 ITRS • There has been an unprecedented acceleration in MOSFET gate length scaling! In many instances, FEP processes have not kept pace, resulting in compromised device performance expectations. This is reflected in the 2001 FEP & PIDS requirements and difficult challenges
FEP Near Term Difficult Challenges For the years up to and including 2007, with DRAM 1/2 Pitch 65nm, and MPU physical gate length 25nm
Near Term Difficult Challenges 1 New gate stack processes and materials for continued planar MOSFET scaling • Remains the number one FEP priority 2 Critical Dimension and MOSFET effective channel length (Leff ) Control 3 CMOS integration of new memory materials and processes 4 Surfaces and Interfaces; structure, composition, and contamination control 5 Scaled MOSFET dopant introduction and control
Challenge #1 New Gate Stack Processes- Issues • Extend oxynitride gate dielectric materials to ~0.8-1nm EOT for high-performance MOSFETS • Introduce and integrate high- gate stack dielectric materials for low operating power MOSFETS • Control boron penetration from doped polysilicon gate electrodes • Minimize depletion of dual-doped polysilicon electrodes • Possible introduction of dual metal gate electrodes with appropriate work function (toward end of period) • Metrology issues associated with gate stack electrical and materials characterization
Gate Stack Challenges Direct tunneling currents limit allowable gate oxide thickness reduction, thereby limiting gate capacitance and gate control over channel charge Electrical depletion of doped polysilicon results in unwanted parasitic capacitance that limits gate control of channel charge Earlier “red wall” for low power results from lower allowed tunneling curents
Challenge #2 CD & Leff Control:Issues • Control of gate etch processes to yield a physical gate length that is smaller than the printed feature size, while maintaining 15% 3- control of the combined lithography and etch processes • Control of profile shape, line and space width for isolated, as well as closely-spaced fine line patterns • Control of self-aligned doping introduction process and thermal activation budgets to yield ~ 25% 3- Leff control • Maintenance of CD and profile control throughout the transition to new gate stack materials and processes • Metrology
Trim Resist Etch Gate Poly Example 150nm Example 100nm Open Hardmask Photoresist Hardmask Gate Poly Gate Oxide Substrate Resist Trim Process Sequence
Challenge #3 CMOS Integration of New Memory Materials: Issues • Development & Introduction of very high- DRAM capacitor dielectric layers • Migration of DRAM capacitor structures from Silicon-Insulator-Metal to Metal-Insulator-Metal • Integration and scaling of ferroelectric materials for FeRAM • Scaling of Flash inter-poly and tunnel dielectric layers may require high- • Limited temperature stability of high- and ferroelectric materials challenges CMOS integration
Technology Migration of Stack Capacitor 130nm 100nm 80nm 65nm MIS MIM MIM MIM Metal Barrier Metal Perovskite epi-BST BST TiN Ta2O5 Poly Si
FLASH Memory Control Gate Interpoly Oxide Floating Gate Tunnel Oxide Source Drain Operating Principle: Charge stored on the floating gate (a bit) , will determine whether a voltage applied to the control gate turns the MOSFET on or off. (read)
FLASH Roadmap Issues: Scaling of the NOR L gate Tunnel oxide must be thick enough to assure charge retention, but thin enough to allow lower write voltage Interpoly oxide must be thick enough to assure charge retention bu thin enough assure almost constant coupling ratio, making charge retention difficult.
Challenge #4 Surfaces & Interfaces: Issues • Contamination, composition and structure control of channel/gate dielectric interface • Contamination, composition and structure control of gate dielectric/gate electrode interface • Interface control of DRAM capacitor structures • Maintenance of surface and interface integrity through full-flow CMOS process • Statistically significant characterization of surfaces having extremely low defect concentrations • Starting materials • Pre-gate cleans
Challenge #5 Scaled MOSFET Doping: Issues • Doping and activation processes to achieve source/drain parasitic resistance that is less than ~16-20% of ideal channel resistance (=Vdd/Ion) • Control of parasitic capacitance to achieve less than ~19-27% of gate capacitance with acceptable Ion and short channel effect • Achievement of activated doping concentration greater than solid solubility levels in dual doped polysilicon gate electrodes • Formation of continuous self-aligned silicon contacts over shallow source/drain regions • Metrology issues associated with 2-D doping profiling
Scaled MOSFET Parasitic Resistance Elements Spreading and Accumulation resistances Extension Sheet Resistivity Contact Junction Sheet Resistivity Contact Resistivity
Parasitic Capacitance Elements Gate/Drain Overlap Capacitance Halo/Extension Junction Capacitance Contact Junction Capacitance
FEP Long Term Difficult Challenges For the years beyond 2007, with DRAM 1/2 Pitch < 65nm, and MPU physical gate length <25nm
Long Term FEP Challenges • Continued scaling of planar CMOS devices • Introduction and CMOS integration of non-standard double-gate MOSFET devices • These devices may be needed as early as 2007 • Increased allocation of long term research resources would be highly desireable • Starting material alternatives beyond 300mm • New memory storage cells, storage devices and memory architectures • Surfaces and Interfaces; structure, composition, and contamination control
Challenge #1- Continued Planar MOSFET Scaling; Issues • Higher- gate dielectric materials • Dual metal gate electrodes with appropriate work function • Possible single drain MOSFET’s with elevated contacts • CMOS Integration consistent with higher- temperature constraints • CD and Leff control • Chemical, electrical, and structural characterization
Challenge #2 Dual-Gate MOSFETS: Issues • Selection and characterization of optimum device types • Device performance and reliability characterization • CMOS Integration with other devices, including planar MOSFETS • Introduction, characterization, and production hardening of new FEP unit processes • Metrology
Challenge #3 Starting Material Alternatives Beyond 300mm: Issues • Future productivity enhancement needs dictate the requirement for a next generation, large substrate material • Historical trends suggest that the new starting material have nominally 2X present generation area, e.g. 450mm • Cost-effective scaling of the incumbent Czochralzki crystal pulling and wafer slicing process is questionable • Research is required for a cost-effective substrate alternative
Challenge #4 New Memory Devices; Issues • Scaling DRAM storage cells beyond 6F2 and ultimately to 4F2 • Possible further scaling of Flash memory interpoly- and tunnel-oxide thickness • FeRAM storage cell scaling • Introduction of new memory types and storage concepts
Challenge #5 Surface & Interface Control; Issues • Achievement and maintenance of structural, chemical, and contamination control over surfaces and interfaces that may be horizontally or vertically oriented relative to the chip surface • Statistically significant characterization of surfaces and interfaces having extremely low defect counts • Metrology and characterization of surfaces and interfaces that may be horizontally or vertically oriented relative to the chip surface.
July 2001 FEP & PIDS ITWG FeRAM Roadmap Here’s a newcomer… S. Kawamura (FEP)
Why FeRAM? • FeRAM has the following outstanding features: • Non-volatility • Low voltage (power) operation • High speed • High Endurance • Capable of high levels of integration • cell size similar to DRAM
FeRAM Roadmap (version 7.0)
Assumptions (1) Feature Size: 0.35mm expected to be available in early 2002, 0.25mm in 2003. x0.7 every 1-3 years. Memory Capacity: Intend to be aggressive to establish FeRAM market. x4 every 1-3 years.
Storage Node Ferro. Film Plate (Planar) Plate Ferro. Film Storage Node (Stack) Assumptions (2) Cell Size: planar stack (x 0.6) 2T2C 1T1C (x 0.6) Switching Charge Qsw: Constant DVbitline=140mV for sensing Qsw=Cbitline x DVbitline
Evolution in Cell Structure Stack Cell (COB) Planar Cell 3D Capacitor Bit Line Bit Line (Polycide, W, etc.) Stack Cell (CUB) Bit Line (Polycide, W, etc.) Bit Line Capacitor Metal Word Line W, etc. Al Ferroelectic Film Pt, IrO2, etc. (Polycide, W, etc.)
FeRAM vs. DRAM Giga scale integration will be available with a 3D capacitor Capacity (Mb) Plate Ferro. Film Storage Node 3D 1T1C Year
DVbitline Estimation Based on DRAM roadmap, DVbitline estimated to be 140mV.
Qsw and Capacitor Structure Qsw/2Pr=Required Capacitor Area> Projected Capacitor Size3D.
Issues (1) In order to enjoy(Lambs) “The Silence of the (other)RAM’s,” reliability comes first to be focused on, followed by application and cost.
Issues (2) Ferroelectric materials: Should be stable under thermal budgets. Usually being used with some dopants. *) Since the PZT contains the lead, it may pose a problem from the viewpoint of ESH. #) Chemical Solution Deposition PZT:Pb(Zr,Ti)O3, SBT:SrBi2Ta2O9, BLT:(Bi,La)4Ti3O12
Issues (3) Fatigue: More than 1E+15 cycles are required to compete with SRAM and DRAM. Practical testing is critical.
Issues (4) Application: Limited to small capacity (embedded) memory for RFID, Smart Card, etc. Some “killer applications” should be needed to establish FeRAM market. Cost: Not competitive due to large cell size. 1T1C and 3D capacitor are mandatory to reduce cost.