The university has developed an extensive materials synthesis and characterization capability over the last 3 years due to a capital investment program totaling $300M from the State of Texas as well as private sources. All the facilities described below are housed in the new Natural Science and Engineering Research Laboratory (NSERL) building.
1.1. Thin Film Deposition and Characterization
A key capability for the program includes the ability to control and characterize all interfacial regions associated with the high-k dielectric/III-V gate stack. A new, unique multi-module cluster system will be utilized in this program for the fabrication and characterization of dielectric (and contact electrode) films on the III-V substrates.
1.1.1. UHV Deposition and Characterization Cluster System
The system, shown in Figure 1, is capable of thin film deposition using PVD methods including electron beam evaporation, molecular beam deposition, sputter deposition, thermal evaporation, and atomic layer deposition methods. (1) Additionally, in-situ characterization techniques include angle-resolved monochromatic x-ray and ultraviolet photoelectron spectroscopy, Auger electron spectroscopy, ion scattering spectroscopy, atomic force and scanning tunneling microscopy/spectroscopy. The system utilizes 100 mm diameter wafers (for cleanroom process compatibility), and modified sample plates for the various deposition and characterization techniques. Wafers are transported throughout the system in a UHV transfer tube. Each deposition module has substrate heating and rotational capability for control of film uniformity and growth kinetics.
The Molecular Beam Epitaxy Module is equipped with two, 100cc Si-shielded e-beam hearths for Si and Ge thin film deposition. Cross-beam quadrupole mass spectrometers as well as quartz crystal microbalance measurements are utilized to control the deposition flux in an automated control system. An integrated Staib RHEED system equipped with a k-Space image digitization/analysis module provides surface preparation and epi-growth quality information. Wafers can be heated to 1200° C with simultaneous rotation. Effusion cells for p-type and n-type dopants are also available on the module. Ports for optical probes, such as ellipsometry, are available on the system.
The Sputter Deposition Module is equipped with four 600W, confocal RF sputter magnetron sources to enable co-sputtering and combinatorial thin film composition studies with 2% thickness uniformity. Wafers can be heated to 1000°C in a reactive (O2) ambient for deposition of thin films. Wafers can also be rotated in-situ for wafer backside deposition. Gas injection is controlled through 4 channel mass flow controller manifold, and pumping is controlled with an automated throttle valve to enable reproducible film deposition.
BELOW: [Figure 1: Comprehensive UHV deposition and character-ization cluster system at UT-Dallas showing various modules.]
The Molecular Beam Deposition/Metal Deposition Module is an exact copy of the MBE Module, but equipped with a 4-pocket (8 cc) e-beam evaporation hearth for various metal depositions as well as 2 effusion cells for high-k oxide growth (e.g. Gd and Ga) and a QCM for flux measurement. Wafers can be heated to 1000°C under simultaneous rotation during deposition, and a shadow mask structure can be accommodated for in-situ fabrication of MIS structures on the wafer. This module is also configured for RHEED analysis and is equipped with a hydrogen cracker cell for surface preparation as well as a plasma source for film deposition/post deposition treatments. Oxygen exposure can be backfilled to the chamber through a leak valve on the cracker cell. Additionally, a plasma source is available to generate reactive species during (and after) oxide deposition. As a part of the GOALI collaboration, this module will also be equipped with the in-situ optical Optical-based Flux Monitoring (OFM) system developed by IntelliEPI, described in detail below, for the control of the high-κ oxide growth.
The Analytical Module is equipped with an array of surface sensitive analytical techniques including monochromatic X-ray Photoelectron Spectroscopy, Ultraviolet Photoelectron Spectroscopy, Scanning Auger Electron Spectroscopy, Low Energy Ion Scattering Spectroscopy, and Scanning Probe Microscopy. Wafers are accommodated on the associated sample holder. Small samples (2.5 cm diameter) can also be separately introduced and characterized in the analytical module under heating and cooling conditions for growth kinetic studies, as well as depth profiling utilizing either angle-resolved XPS or Ar-ion depth profiling with in-situ sample rotation for better depth resolution. For in-situ film morphology studies, the AFM/STM module is capable of accommodating a 100mm wafer.
A commercial Atomic Layer Deposition module has been integrated onto the system. The Pisosun ALD reactor and the associated buffer chamber enable the detailed study of thin films deposited by this technologically important technique. The buffer chamber provides the ability to transport wafers through the system and surmount the pressure gap between the ALD reactor and the UHV system for subsequent surface characterization or thin film PVD deposition. Additionally, the ALD reactor is capable of direct wafer/sample insertion as well. Up to three precursor sources are available on this system for liquid, gas and solid precursors.
The attached Annealing Process Module permits thermal processing of wafers up to 700°C under various ambients which are relevant for post deposition treatments and ex-situ device electrical characterization (such as forming gas, UV/O3, as well as O2, N2, Ar, etc.).
The laboratory housing the system is also equipped with wet chemical preparation facilities for wafer surface preparation.
(1) The system was assembled by Omicron Nanotechnology, GMBH. See: http://www.omicron.de/
(2) The ALD reactor is made by Picosun, Oy.: http://www.picosun.com/ Picosun’s founders were among the founders of Michrochemistry in Finland who invented the ALD techniques and developed the first ALD tools in 1974.
1.1.2. Molecular Beam Epitaxy
A new integrated, heterogeneous MBE deposition system has been established linked together with a UHV transfer module, as shown in Figure 2. The first system, V80S, is designed to grow undoped and doped group-IV compounds such as Si, Ge, and strained Si/Ge superlattices structures. Doping n and p-type is done with Sb and B respectively.
LEFT: [Figure 2 Three MBE growth chamber layout.]
The vertical growth chamber in this system incorporates two electron-beam evaporators for Si and Ge and two effu¬sion cells for doping. In addition it has a preparation chamber with a high temperature heating stage. The second chamber, V80H, features a horizontal growth chamber, eight effusion cells, and a preparation chamber. It is designed to grow II-VI materials such as BeTe, BeSe, ZnSe, ZnS, BeTeSe, and CdSeTe, epilayers as well as quantum well and superlattice structures. It also has an atomic N plasma source for p-doping and ZnCl2 for n-doping. The third system is identical to the second one; however, this system is used to grow III-V materials such as GaAs, InGaAs, and AlGaAs and to dope with Be and Si. VG Instruments built all three systems. They are fully controlled by computer and equipped with high-capacity, vacuum-pumping units that operate at a base pressure in the low 10(–10) mbar range without liquid nitrogen cooling. Each growth chamber is equipped with various types of analytical tools such as RHEED and QMS. Research associates handle the technical operation and maintenance of this facility along with graduate students and technical-level personnel.
1.1.3. Optical Surface Infrared Spectroscopy
The optical spectroscopy laboratory integrates a number of optical techniques (infrared, Raman, UV-vis spectroscopy and spectroscopic ellipsometry) with home made chambers and reactors for in-situ studies of surface modification, thin film growth and nano-materials characterization. It includes four Ultra High Vacuum (UHV) chambers and five Atomic Layer Deposition reactors, each one interfaced to a separate FTIR spectrometer. Two UHV chambers are equipped with Low Energy Electron Diffraction (LEED), Auger Electron Spectrometers (AES), Mass spectrometers, IR windows, evaporators, W filaments to crack hydrogen, metal effusion sources, sputter guns, manipulators with cooling (77K) and heating (2000K). One chamber is specifically designed for grazing incidence IR spectroscopy and currently used to study metal surfaces. Another chamber features a load lock with an internal chamber to perform MOCVD, to prepare for instance III-V surfaces with appropriate stoichiometries (i.e. reconstructions). All ALD reactors are designed for in-situ IR spectroscopy and mass spectrometry. Three ALD reactors can in addition accommodate a quartz crystal monitor, a mass spectrometer, and a Woolam M2000D ellipsometer (193-1000nm) for in-situ studies of growth. Three all-aluminum reactors have also been built and are interfaced to IR spectrometers to study aggressive vapor phase processing of semiconductor and metal surfaces (e.g. XeF2 etching).
Three Specac high pressure infrared cells operating between 300 and 1100K for a pressure range 0-60 atm are interfaced with IR interferometers. These cells can be used both in transmission and reflection and are currently being used to study H2 in metal organic framework materials. Chambers to study surface processes are routinely configured, such as the one below used to study the oxidation of graphene by remote plasma and/or ozone.
In addition optical probes dedicated to in-situ studies, the lab is equipped with a Horiba Jobin Yvon UVISEL ellipsometer (190-2000nm ), a Thermo Nicolet micro and macro Almega XR Raman spectrometer, a Veeco Dimension 3100 atomic force microscope, a Perkin Elmer XPS spectrometer, a TGA instrument, several ovens, a high purity, recirculating MBraun 20G dual glove boxes (with one box for an FTIR spectrometer), an infrared microscope and an FT-Raman instrument, and a Thermo Legend-Mach 1.6 centrifuge.
The infrastructure of the lab includes four hoods with two high purity de-ionized water polishers, a burn box to neutralize and exhaust all toxic gases (reactants and products used for ALD, CVD and other vapor phase processes), gas sensors for all potentially dangerous gases including H2, and explosion proof gas cabinets for all dangerous gases, including H2.
1.1.4. Electron Microscopy Facilities
For the nanoscale analysis of high-k/III-V stack structures, UTD is well equipped in state-of-the-art electron microscopy as well. A focused ion beam system available in the Advanced Microscopy Laboratory is a FEI Nova 200 NanoLab which is a dual column SEM/FIB. It combines ultra-high resolution field emission scanning electron microscopy (SEM) and focused ion beam (FIB) etch and deposition for nanoscale prototyping, machining, 2-D and 3-D characterization, and analysis. Five gas injection systems are available for deposition (e.g. Pt, C, SiO2) and etching (e.g. Iodine for metals, and a dielectric etch). The FIB will be critical for TEM sample preparation of III-V compounds. Nanoscale chemical analysis is performed with energy dispersive X-ray spectroscopy (EDS). The secondary electron image resolution at the dual beam coincidence point is 1.5 nm at 15 kV. The FIB optics have better than 7 nm resolution at 30 kV. A high resolution digital patterning system controlled from the user interface is also available. Predefined device structures in Bitmap format can be directly imported to the patterning system for nanoscale fabrication. The FEI Nova 200 is also equipped with a Zyvex F100 nano-manipulation stage, which includes four manipulators with 10 nm positioning resolution. The four manipulators can be fitted with either sharp whisker probes for electrically probing samples or microgrippers for manipulating nanostructures as small as 10 nanometers. Students are trained to operate this instrument routinely by a dedicated full time staff member.
FAR LEFT: [Figure 3. Thin film configuration for Ultima-III XRD system]
LEFT: [Figure 4. Small spot Rapid-Spider XRD system with image plate detection]
High Resolution Transmission Electron Microscopy (HRTEM) is also available in the Advanced Microscopy Laboratory at UTD and provides powerful and essential tools to the program and also serves as a powerful vehicle to bring state-of-the art nanoscale materials research into the classroom. The facility operates and maintains two state-of-the-art transmission electron microscopes (TEM), and a host of sample preparation equipments. It also provides microscopy computing and visualization capabilities. Techniques and equipment which will be leveraged by the program includes the following: (i) High Resolution Structural Analysis - The high-resolution imaging TEM is a JEOL 2100 F which is a 200kV field emission TEM. Its capability includes atomic scale structural imaging with a resolution of better than 0.19 nm, and in-situ STM/TEM analysis. Students are trained to operate this instrument routinely by a dedicated full time staff member. (ii) High Resolution Chemical and Electronic Structure Analysis – The high resolution analytical TEM is a second JEOL 2100F field emission TEM/STEM equipped with an energy dispersive x-ray spectrometer (EDS), an electron energy loss spectrometer (EELS), and a high angle Z-contrast imaging detector. This instrument performs chemical and electronic structure analysis with a spatial resolution of better than 0.5 nm in EELS mode and is also capable of spectrum imaging and mapping. The image resolution in the chemically sensitive Z-contrast scanning TEM (STEM) mode is ~0.14 nm. Its capability also includes in-situ cryogenic cooling and heating, and a computer control system for remote microscopy operation.
1.1.5. X-ray Diffraction Suite
For the study of film microstructure and epitaxial quality, a new X-ray diffraction suite has been acquired by UTD to support nanotechnology thin film materials research. A Rigaku Ultima III X-ray Diffractometer system is available for thin film diffraction characterization (Fig. 2). The system is equipped with a cross beam optics system to permit either high-resolution parallel beam with a motor controlled multilayer mirror, or a Bragg-Brentano para-focusing beam which are permanently mounted, pre-aligned and user selectable with no need for any interchange between components. Curved graphite crystal or Ge monochrometers are also available for high-resolution XRD measurements. An integrated annealing attachment permits the in-situ examination of film structure up to 1500°C.
The instrument enables a variety of applications including in-plane and normal geometry phase identification, quantitative analysis, lattice parameter refinement, crystallite size, structure refinement, residual stress, density, roughness (from reflectivity geometries), and depth-controlled phase identification. The advanced thin film attachments enable precise sample alignment for x-ray reflectivity, grazing-incidence x-ray diffraction, epitaxial film concentration and structure analysis using reciprocal space mapping and rocking curve measurements. Detection consists of a computer controlled scintillation counter. Sample sizes up to 100 mm in diameter can be accommodated on this system.
A Rigaku Rapid-Spider Image Plate Diffractometer system is also available for small spot (30μm – 300μm) XRD work (Fig. 3). The digital image plate system enables the acquisition of diffraction data over a 2θ=204° angle with a rapid laser scanning readout system. An integrated annealing attachment permits the in-situ examination of film structure up to 900°C on this system.
A complete set of new control software, database, and analysis workstations is associated with these new systems. Students are trained to operate these instruments routinely by a dedicated full time staff member.
For electrical measurements, we will fabricate capacitors and long channel transistors in this program. The Cleanroom Research Laboratory, located in the new Natural Science and Engineering Research Laboratory (http://www.utdallas.edu/eecs/cleanroom/) will be utilized to support this program. The total area of this facility includes 5,000 sq. ft. of class 10,000 space. This facility contains semiconductor processing tools including optical, e-beam, and nanoimprint lithography, chemical processing hoods, evaporation, sputter and chemical vapor deposition systems, as well as a wide variety of material and processing diagnostics. The total tool count is currently at 70. The facility is supported by an experienced staff of 3 professionals and 5 technicians. The professional staff includes the cleanroom associate director, Mr. Wallace Martin, with more than 37 years of experience in semiconductor R&D. Process engineering support is provided by Dr. Gordon Pollack and Dr. Roger Robbins with a combined 55 years of experience in semiconductor R&D. All of the technician support staff members have extensive cleanroom operations and tool experience as well.
The lithography component in the cleanroom facility consists of a Quintel contact printer, a Karl Suss optical aligner with backside alignment capability, and a nanoimprint lithography tool. The ability to make photomasks in-house allows us to make design changes quickly, and for the students to try new concepts with a minimal cost. A Heidelberg DWL66 Laser Lithography Tool permits the fabrication of up to 5” masks as well as direct write capability on wafers with .6 micron resolution. A Quintel aligner is also available with a G-line contact printer with ~ 1 micron resolution and backside alignment capability (~1 micron). It will accept up 150 mm wafers. For nanoscale features, the direct write capability of the LEO SEM is utilized and described below.
Exposed resist is developed in 2 versatile “CPK” developers using spray and spin wet processes. One CPK is configured to etch Chrome photomasks and caustic develop of positive photoresist. The other CPK unit is configured for solvent develop of negative photoresist. This technology is highly automated and contains up to 99 process programs. These tools produce developed substrates nearly free of particles.
The thin-film deposition component of the lab includes a Uniaxis Plasma Enhanced CVD (up to 150 mm wafer), a CHA Mark 50 E-beam evaporator (3 guns with co-evaporation capability), two E-beam evaporators (each fitting up to 150 mm wafers), a Denton thermal evaporator, a new AJA four-head sputter deposition system (designed for 100 mm wafers) and a “Tystar” Low Pressure Chemical Vapor Deposition system. The LPCVD tool is designed for either 100-150 mm wafers and has 4 tubes. Deposition of low stress silicon nitride, polysilicon and silicon dioxide films is available. For atomic layer deposition, a Cambridge NanoTech Savannah 200 ALD system is available.
Current plasma etch capability includes the following systems: Oerlikon Versaline chlorine-based ICP etcher, Oerlikon Versaline fluorine-based ICP etcher with DSE (deep Silicon etch) capability a “Technics” RIE for 100-125 mm wafers, a Plasmaline barrel asher/etcher, and a MARCH PX250 asher/etcher.
There are several anneal and oxidation furnaces available including a Tystar 4 tube atmospheric furnace configured for oxidation and dopant diffusion, 4 Minibrute tube furnaces (100mm), two MPT RTA systems, and a JetFirst 200 Rapid Thermal Anneal (RTA) system (up to 200 mm wafers).
The clean room diagnostics include, a spectroscopic ellipsometer, optical microscopes ( Leica INM 200 and Leica INM 100), ALESSI 4 point probe, and a high resolution AFM, a Thermoelectron FTIR with grazing attachments, a Nanometric Nanospec 6100 film thickness measurement system, a Veeco Dektak VIII profilometer and a Toho film stress measurement tool. A new $1M Field emission SEM (Zeiss LEO Supra40) with e-beam writing capability, Zyvex nanomanipulator/prober, secondary, STEM, backscattering detectors, as well as EDAX is also available for students in this facility.
A complete list of tools can be found at http://www.utdallas.edu/research/cleanroom/manuals/index.html.
For the electrical characterization, a Cascade Summit series probe station with integrated environmental control capable of probing structures on wafers (up to 200 mm diameter) over a temperature range of -65 to 200 °C (Fig. 4) will be used.
LEFT: [Figure 5. Cascade Summit probe station with environmental chamber.]
The probe station provides for current measurement down to fA and capacitance measurement down to tens of fF. A Lakeshore Cryogenic low temperature probe station which expands the accessible temperature range and permit device level characterization on structures down to temperatures of ~4.5K. The facility has an Agilent 4155 semiconductor parameter analyzer, an Agilent 4284A LCR meter, an Agilent 81110A pulse/pattern generator, a Tektronix DP07104 digital oscilloscope, Keithley 4200 semiconductor parameter analyzers, a Keithley 590 capacitance-voltage meter and a variety of other electronics that are integrated with a low current switch matrix. This equipment permits almost any device electrical test for MOS capacitors and transistors including current-voltage, capacitance and conductance as a function of voltage and frequency, pulsed current-voltage to characterize transient response, charge-pumping to measure dielectric/semiconductor interfacial defects, and automated reliability characterization for stressing a device while intermittently measuring any of the above electrical characteristics. Fig. 5 illustrates MOS devices fabricated at UTD with good performance and intrinsic reliability.
A cryoelectronics laboratory has also been assembled consisting of four major equipment items: a superconducting cryostat and closed cycle crysostat for magneto spectroscopy. The superconducting cryostat includes a Liquid helium dewar and homebuilt probes, a 50.8 mm Dia. superconducting solenoid (0 - 5 T, with persistent switch) and is capable of a measurement temperature range of 2.0 K to 300K. The closed cycle cryostat for magneto spectroscopy is manufactured by Advanced Research Systems, Inc. and is a Displex™ Plus Closed Cycle System Model CSW-202+ with tail section for insertion in magnetic pole pieces. The system has a cooling capacity of 50 mW at 4.2 K, and a highest operational temperature of 350 K and is mounted on electromagnet with moveable pole pieces (water cooled, 0 - 1.0 T). The laboratory also has a UV-visible monochromator (Newport C-130 UV/VIS 1/8 m Cornerstone) with a motorized scan range of 200 nm – 1600 nm. There is also associated free space optics and a chopper detection system.
A computer controlled I – V electronic measurements and data recording system is also utilized based upon instrumentation manufactured by Keithley and HP.
ABOVE: [Figure 6: Illustration of UTD’s device fabrication capability. (a) SEM image of a UTD fabricated MOSFET. (b) Linear Id-Vg and effective channel mobility of an n-channel FET with 3 nm SiO2 gate dielectric. (c) Breakdown voltage distribution of 30 nm SiO2 indicating intrinsic reliability. (d) C-V of a HfO2/SiO2 stack.]