ESH Benign Processes for he Integration of Quantum Dots (QDs) PIs: Karen K. Gleason, Department of Chemical Engineering, MIT Graduate Students: Chia-Hua Lee: PhD Candidate, Department of Material Science and Engineering, MIT Wyatt Tenhaeff, Ph.D Candidate, Department of Chemical Engineering, MIT (NSF Fellow) SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 1
Motivation Physical limitations of silicon-based devices inhibit continued innovation in IT, communications, and electronics. Conventional micro-fabrication techniques are reaching the limits of their capabilities, while fabrication costs and complexity continue to grow. Breakthroughs for building electronics at the nanoscale requires new materials and new manufacturing concepts. Achieving semiconducting behavior through nanoparticles eliminates the need high quality Si substrates avoids energy intensive fabrication of high purity silicon wafers. allows for inexpensive, lightweight flexible substrates compatible with roll-toroll processing. SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 2
Quantum Dots (QDs) Nanocrystals of a semiconductor compound Quantum dot size is not limited by lithography Diameters in the 1 to 10 nm length scale Electrons are quantum confined in 3D Enable new devices and markets such as quantum information processing: spin-transistors, nanomagnets quantum computing electron spin-based memory. The Quantum Dot SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 3
QDs in future electronics Linear and nonlinear quantum transport phenomena Transitions among quantum confined states Control over the behavior of a single or a few electrons as well as that of a single or a few photons Switching device structure with the potential for much higher speeds, lower power consumption and higher packing densities than CMS transistors (Alignment of Epitaxial Quantum Dots: Springer, 2007) resonant tunneling transistors (RTDs single-electron transistors (SETs) spin transistors Next generation memory devices (M. Geller et. At: Appl. Phys. Lett. 92, 092108, 2008) storing one terabyte (1000 gigabytes) of data per square inch write information to this memory in just 6 nanoseconds SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 4
QDs ptoelectronics Frequency of light emission depends on QD size Narrow emission band High quantum yields: 85 % Broad excitation spectra Chemical/photo stability Applications tunable IR-UV lasers and LEDs display luminophores optical electro-modulation, optical limiting DNA site markers efficient sensors of explosives and toxic materials. C. B. Murray, C. R. Kagan, and M. G. Bawendi, Annu. Rev. Mater. Sci., 2000. 30:545 610 SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 5
Detecting a single photon Detectors with the capability to directly measure the photon number of a pulse of light enable linear optics quantum computing, affect the security of quantum communications, and can be used to characterize, and herald non-classical states of light. E. J. Gansen et. al, Nature Photonics 1, 585-588 (2007) SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 6
ESH Nanoparticles which are not confined to a surface film are free to transport by diffusion and convection. The size (typically <10 nm) limits the ability to be filtered or separated efficiently with current technology. Early consideration the ESH life cycle in the design and development of a new material reduces the total cost of introducing and using a technology compared to revisions made closer to high volume manufacturing. Developing technology separately from ESH impact and evaluating ESH impact without the capability to affect a technology is inefficient since the two are intimately connected. SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 7
Scope Processes for tethering QDs to surfaces with precise spatial control is required in order to exploit the novel electronic properties of these nanoparticles ESH benign fabrication methods are desired which are compatible with wafer processing and also with flexible substrates. The use of flexible substrates is required for roll-to-roll processing, which is a high-volume, low-cost manufacturing method. White paper for 2009 with Dr. Anthony Muscat - ESH benign QD synthesis Dr. Mark Riley development and implementation of ESH assesment tools SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 8
Initiated CVD of Functionalizable Polymers Flow Control Resistivel y Heated Filaments Pressure Gauge Throttling Butterfly Valve initiator Flow Control monomer 1 Flow Control monomer 2 Reactor Quartz Top Recirculating Coolant Pump insitu thickness monitoring by interferometry or quartz crystal microbalance To Exhaust Substrates remain near room temperature during coating Functional groups in icvd films can be used to covalently tether nanoparticles SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 9
Fabrication Strategy Sub-50 nm patterns of a functional polymer on Si wafer or flexible substrate (avoid use of conventional lithography) Covalent tethering of QDs SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 10
Tethering Chemistry n + H 2 N NH 2 QD NH2 NH 2 NH 2 Functional polymer layer H 2 N NH 2 QD NH2 NH 2 DI water, 60 o C, 15 hr N + H 2 oven, 100 o C, overnight n SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 11
icvd functional polymer layer 12 C: 3 n per unit (80% carbon) Styrene Maleic Anhydride Poly(styrene-alt-maleic anhydride) (PSMa) 90.0 %Carbon 80.0 70.0 XPS Survey Scan: perfect alternation Styrene Flow Rate 5 sccm 10 sccm 20 sccm ESH: Bulk PSMA is widely used for products such as cooking utensils and coatings on ingestible drugs 60.0 2 4 6 Maleic Anhydride Flow Rate (sccm) W.E. Tenhaeff and K.K. Gleason Langmuir 23, 6624 (2007). SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 12
QD Attachment to icvd PSMa QD Size ~ 5 nm UV spectrum Postultrasonication Polymer / QDs H 2 N NH 2 NH 2 QD N NH 2 QDs n Polymer 450 500 550 600 650 700 750 800 ( nm ) SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 13
CNT masks for patterning icvd PSMa CNTs PStMa Si wafer patterned polymer patterned QDs Spin casting of CNT masks on the icvd PSMa polymer thin film xygen plasma etching Removal of CNT masks Quantum dots tethered to surface SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 14
AFM Height Image CNTs P(StMa) pattern Si wafer SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 15
Carbon Nanotube (CNT) masking results (1) After spin-casting of CNTs (CNT~ 50-60 nm) 100 nm (2) Polymer pattern ~ 40 nm (3) Polymer pattern ~ 35 nm 100 nm (Etching time: 35 s) After etching and partial removal of the CNTs Pattern in polymer is smaller than CNT diameter CNT~ 60 nm 100 nm 100 nm (Etching time: 40 s) SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 16
(CNT~ 60 nm) Polymer pattern ~ 40 nm 100 nm (Etching time: 30 s) (CNT~ 20 nm) 100 nm Pattern sizes depend on the CNT diameters and the etching time 100 Polymer nm pattern ~ 40 nm Polymer pattern ~ 20 nm 45 40 35 linewidth 30 25 100 nm 100 nm (Etching time: 40 s) (Etching time: 60 s) 20 15 15 20 25 30 35 40 45 50 55 60 65 Etching Time (s) SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 17
Fluorescence Microscope Each florescent dot represents a bunch polymer/qd patterns 40 µm 40 µm 40 µm P(StMa) ICVD polymer film P(StMa) /QD blanket film P(StMa) /QD patterned film Polymer/QD pattern SEM images of polymer/qd pattern 100 nm SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 18
CNT Alignment Strategy (a) Polar area Non-polar area (b) CNT solution Droplets (c) (on polar area) (d) SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 19
Carbon Nanotube (CNT) Alignment Microcontact stamping Ink (1-Hexadecylamine) stamp substrate (Si wafer) Pattern transfer NH 2 NH 2 H H NH 2 H The pattern transfer is based on the formation of Hydrogen Bonds between the amine groups 1-Hexadecylamine and the hydroxyl groups of the substrate. SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 20
AFM Images SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 21
Future Plans Use functional icvd polymers to align the carbon nanotubes Fabricate simple quantum dot devices using the novel patterning strategies Demonstrate the performance of high resolution devices on flexible, low cost, light weight substrates. SRC/SEMATECH Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 22