Query: Optically monitoring and controlling nanoscale topography during semiconductor etching

Candidate papers:

abstract: Semiconductor etching can now be monitored in real time at nanoscale resolution using a non destructive optical imaging technique that combines a conventional microscope with a compact Mach Zehnder interferometer. Developed by Chris Edwards, Amir Arbabi, Gabriel Popescu, and Lynford Goddard at the University of Illinois at Urbana Champaign in the United States, epi diffraction phase microscopy makes it possible to collect three dimensional videos of semiconductor fabrication processes using a CCD camera. The approach is able to measure etch rates at each location across the sample with a resolution of 0.085 nm s 1 per pixel. Such an in situ monitoring capability could be useful for improving the manufacturing quality of a wide variety of semiconductor devices.
author_names: Chris Edwards

Amir Arbabi

Gabriel Popescu

Lynford L Goddard
title: Optically monitoring and controlling nanoscale topography during semiconductor etching
year: 2012

author_names: Christopher J Edwards

Amir Arbabi

Gabriel Popescu

Lynford L Goddard
title: Erratum: Optically monitoring and controlling nanoscale topography during semiconductor etching (Light: Science Applications (2012) 1(e30) doi:10.1038/lsa.2012.30)
year: 2012

abstract: Rapid progress in the synthesis and processing of materials with structure on nanometer length scales has created a demand for greater scientific understanding of thermal transport in nanoscale devices, individual nanostructures, and nanostructured materials. This review emphasizes developments in experiment, theory, and computation that have occurred in the past ten years and summarizes the present status of the field. Interfaces between materials become increasingly important on small length scales. The thermal conductance of many solid solid interfaces have been studied experimentally but the range of observed interface properties is much smaller than predicted by simple theory. Classical molecular dynamics simulations are emerging as a powerful tool for calculations of thermal conductance and phonon scattering, and may provide for a lively interplay of experiment and theory in the near term. Fundamental issues remain concerning the correct definitions of temperature in nonequilibrium nanoscale systems. Modern Si microelectronics are now firmly in the nanoscale regime experiments have demonstrated that the close proximity of interfaces and the extremely small volume of heat dissipation strongly modifies thermal transport, thereby aggravating problems of thermal management. Microelectronic devices are too large to yield to atomic level simulation in the foreseeable future and, therefore, calculations of thermal transport must rely on solutions of the Boltzmann transport equation; microscopic phonon scattering rates needed for predictive models are, even for Si, poorly known. Low dimensional nanostructures, such as carbon nanotubes, are predicted to have novel transport properties; the first quantitative experiments of the thermal conductivity of nanotubes have recently been achieved using microfabricated measurement systems. Nanoscale porosity decreases the permittivity of amorphous dielectrics but porosity also strongly decreases the thermal conductivity. The promise of improved thermoelectric materials and problems of thermal management of optoelectronic devices have stimulated extensive studies of semiconductor superlattices; agreement between experiment and theory is generally poor. Advances in measurement methods, e.g. the 3o method, time domain thermoreflectance, sources of coherent phonons, microfabricated test structures, and the scanning thermal microscope, are enabling new capabilities for nanoscale thermal metrology.
author_names: David G Cahill

W Ford

Kenneth E Goodson

Gerald Dennis Mahan

A Majumdar

Humphrey J Maris

Roberto Merlin

Simon R Phillpot
title: Nanoscale thermal transport
year: 2003

abstract: Preface to Third Edition. 1 Resistivity. 1.1 Introduction. 1.2 Two Point Versus Four Point Probe. 1.3 Wafer Mapping. 1.4 Resistivity Profiling. 1.5 Contactless Methods. 1.6 Conductivity Type. 1.7 Strengths and Weaknesses. Appendix 1.1 Resistivity as a Function of Doping Density. Appendix 1.2 Intrinsic Carrier Density. References. Problems. Review Questions. 2 Carrier and Doping Density. 2.1 Introduction. 2.2 Capacitance Voltage (C V) 2.3 Current Voltage (I V) 2.4 Measurement Errors and Precautions. 2.5 Hall Effect. 2.6 Optical Techniques. 2.7 Secondary Ion Mass Spectrometry (SIMS) 2.8 Rutherford Backscattering (RBS) 2.9 Lateral Profiling. 2.10 Strengths and Weaknesses. Appendix 2.1 Parallel or Series Connection? Appendix 2.2 Circuit Conversion. References. Problems. Review Questions. 3 Contact Resistance and Schottky Barriers. 3.1 Introduction. 3.2 Metal Semiconductor Contacts. 3.3 Contact Resistance. 3.4 Measurement Techniques. 3.5 Schottky Barrier Height. 3.6 Comparison of Methods. 3.7 Strengths and Weaknesses. Appendix 3.1 Effect of Parasitic Resistance. Appendix 3.2 Alloys for Contacts to Semiconductors. References. Problems. Review Questions. 4 Series Resistance, Channel Length and Width, and Threshold Voltage. 4.1 Introduction. 4.2 PN Junction Diodes. 4.3 Schottky Barrier Diodes. 4.4 Solar Cells. 4.5 Bipolar Junction Transistors. 4.6 MOSFETS. 4.7 MESFETS and MODFETS. 4.8 Threshold Voltage. 4.9 Pseudo MOSFET. 4.10 Strengths and Weaknesses. Appendix 4.1 Schottky Diode Current Voltage Equation. References. Problems. Review Questions. 5 Defects. 5.1 Introduction. 5.2 Generation Recombination Statistics. 5.3 Capacitance Measurements. 5.4 Current Measurements. 5.5 Charge Measurements. 5.6 Deep Level Transient Spectroscopy (DLTS) 5.7 Thermally Stimulated Capacitance and Current. 5.8 Positron Annihilation Spectroscopy (PAS) 5.9 Strengths and Weaknesses. Appendix 5.1 Activation Energy and Capture Cross Section. Appendix 5.2 Time Constant Extraction. Appendix 5.3 Si and GaAs Data. References. Problems. Review Questions. 6 Oxide and Interface Trapped Charges, Oxide Thickness. 6.1 Introduction. 6.2 Fixed, Oxide Trapped, and Mobile Oxide Charge. 6.3 Interface Trapped Charge. 6.4 Oxide Thickness. 6.5 Strengths and Weaknesses. Appendix 6.1 Capacitance Measurement Techniques. Appendix 6.2 Effect of Chuck Capacitance and Leakage Current. References. Problems. Review Questions. 7 Carrier Lifetimes. 7.1 Introduction. 7.2 Recombination Lifetime/Surface Recombination Velocity. 7.3 Generation Lifetime/Surface Generation Velocity. 7.4 Recombination Lifetime Optical Measurements. 7.5 Recombination Lifetime Electrical Measurements. 7.6 Generation Lifetime Electrical Measurements. 7.7 Strengths and Weaknesses. Appendix 7.1 Optical Excitation. Appendix 7.2 Electrical Excitation. References. Problems. Review Questions. 8 Mobility. 8.1 Introduction. 8.2 Conductivity Mobility. 8.3 Hall Effect and Mobility. 8.4 Magnetoresistance Mobility. 8.5 Time of Flight Drift Mobility. 8.6 MOSFET Mobility. 8.7 Contactless Mobility. 8.8 Strengths and Weaknesses. Appendix 8.1 Semiconductor Bulk Mobilities. Appendix 8.2 Semiconductor Surface Mobilities. Appendix 8.3 Effect of Channel Frequency Response. Appendix 8.4 Effect of Interface Trapped Charge. References. Problems. Review Questions. 9 Charge based and Probe Characterization. 9.1 Introduction. 9.2 Background. 9.3 Surface Charging. 9.4 The Kelvin Probe. 9.5 Applications. 9.6 Scanning Probe Microscopy (SPM) 9.7 Strengths and Weaknesses. References. Problems. Review Questions. 10 Optical Characterization. 10.1 Introduction. 10.2 Optical Microscopy. 10.3 Ellipsometry. 10.4 Transmission. 10.5 Reflection. 10.6 Light Scattering. 10.7 Modulation Spectroscopy. 10.8 Line Width. 10.9 Photoluminescence (PL) 10.10 Raman Spectroscopy. 10.11 Strengths and Weaknesses. Appendix 10.1 Transmission Equations. Appendix 10.2 Absorption Coefficients and Refractive Indices for Selected Semiconductors. References. Problems. Review Questions. 11 Chemical and Physical Characterization. 11.1 Introduction. 11.2 Electron Beam Techniques. 11.3 Ion Beam Techniques. 11.4 X Ray and Gamma Ray Techniques. 11.5 Strengths and Weaknesses. Appendix 11.1 Selected Features of Some Analytical Techniques. References. Problems. Review Questions. 12 Reliability and Failure Analysis. 12.1 Introduction. 12.2 Failure Times and Acceleration Factors. 12.3 Distribution Functions. 12.4 Reliability Concerns. 12.5 Failure Analysis Characterization Techniques. 12.6 Strengths and Weaknesses. Appendix 12.1 Gate Currents. References. Problems. Review Questions. Appendix 1 List of Symbols. Appendix 2 Abbreviations and Acronyms. Index.
author_names: Dieter K Schroder
title: Semiconductor Material and Device Characterization
year: 1990

abstract: A formation process for semiconductor quantum dots based on a surface instability induced by ion sputtering under normal incidence is presented. Crystalline dots 35 nanometers in diameter and arranged in a regular hexagonal lattice were produced on gallium antimonide surfaces. The formation mechanism relies on a natural self organization mechanism that occurs during the erosion of surfaces, which is based on the interplay between roughening induced by ion sputtering and smoothing due to surface diffusion.
title: Formation of Ordered Nanoscale Semiconductor Dots by Ion Sputtering.
venue: Science
year: 1999

abstract: This protocol provides an introduction to soft lithography a collection of techniques based on printing, molding and embossing with an elastomeric stamp. Soft lithography provides access to three dimensional and curved structures, tolerates a wide variety of materials, generates well defined and controllable surface chemistries, and is generally compatible with biological applications. It is also low in cost, experimentally convenient and has emerged as a technology useful for a number of applications that include cell biology, microfluidics, lab on a chip, microelectromechanical systems and flexible electronics/photonics. As examples, here we focus on three of the commonly used soft lithographic techniques: (i) microcontact printing of alkanethiols and proteins on gold coated and glass substrates; (ii) replica molding for fabrication of microfluidic devices in poly(dimethyl siloxane) and of nanostructures in polyurethane or epoxy; and (iii) solvent assisted micromolding of nanostructures in poly(methyl methacrylate)
author_names: Dong Qin

Younan Xia

George M Whitesides
title: Soft lithography for micro and nanoscale patterning
venue: Nature Protocols
year: 2010

abstract: An aluminum coated tapered optical fiber is rigidly attached to one of the prongs of a high Q piezoelectric tuning fork. The fork is mechanically dithered at its resonance frequency (33 kHz) so that the tip amplitude does not exceed 0.4 nm. A corresponding piezoelectric signal is measured on electrodes appropriately placed on the prongs. As the tip approaches within 20 nm above the sample surface a 0.1 nN drag force acting on the tip causes the signal to reduce. This signal is used to position the optical fiber tip to about 0 to 25 nm above the sample. Shear forces resulting from the tip sample interaction can be quantitatively deduced.
author_names: Khaled Karrai

Robert D Grober
title: Piezoelectric tip sample distance control for near field optical microscopes
year: 1995

abstract: Over the last 2 decades, scanning electrochemical microscopy (SECM) has been extensively employed for topographic imaging and mapping surface reactivity on the micrometer scale. We used flat, polished nanoelectrodes as SECM tips to carry out feedback mode imaging of various substrates with nanoscale resolution. Constant height and constant current images of plastic and Au compact disc surfaces and more complicated objects (computer chips and wafers) were obtained. The possibility of simultaneous imaging of surface topography and electrochemical reactivity was demonstrated. Very fast mass transfer at nanoelectrodes allowed us to obtain high quality electrochemical images in viscous media under steady state conditions, e.g. in 1 methyl 3 octylimidazolium bis(tetrafluoromethylsulfonyl)imide (C(8)mimC(1)C(1)N) ionic liquid. Ion transfer based imaging was also performed using nanopipets as SECM tips.
author_names: Francois O Laforge

Jeyavel Velmurugan

Yixian Wang

Michael V Mirkin
title: Nanoscale imaging of surface topography and reactivity with the scanning electrochemical microscope.
venue: Analytical chemistry
year: 2009

abstract: As multistep, multilayer processing in semiconductor industry becomes more complex, the role of cleaning solutions and etching chemistries are becoming important in enhancing yield and in reducing defects. This thesis demonstrates successful formulations that exhibit copper and tungsten compatibility, and are capable of Inter Layer Dielectric (ILD) cleaning and selective Ti etching. The corrosion behavior of electrochemically deposited copper thin films in deareated and non dearated cleaning solution containing hydrofluoric acid (HF) has been investigated. Potentiodynamic polarization experiments were carried out to determine active, active passive, passive, and transpassive regions. Corrosion rates were calculated from tafel slopes. ICP MS and potentiodynamic methods yielded comparable Cu dissolution rates. Interestingly, the presence of hydrogen peroxide in the cleaning solution led to more than an order of magnitude suppression of copper dissolution rate. We ascribe this phenomenon to the formation of interfacial CuO which dissolves at slower rate in dilute HF. A kinetic scheme involving cathodic reduction of oxygen and anodic oxidation of Cu0 and Cu+1 is proposed. It was determined that the reaction order kinetics is first order with respect to both HF and oxygen concentrations. The learnings from copper corrosion studies were leveraged to develop a wet etch/clean formulation for selective titanium etching. The introduction of titanium hard mask (HM) for dual damascene patterning of copper interconnects created a unique application in selective wet etch chemistry. A formulation that addresses the selectivity requirements was not available and was developed during the course of this dissertation. This chemical formulation selectively strips Ti HM film and removes post plasma etch polymer/residue while suppressing the etch rate of tungsten, copper, silicon oxide, silicon carbide, silicon nitride, and carbon doped silicon oxide. Ti etching selectivity exceeding three orders of magnitude was realized. Surprisingly, it exploits the use of HF, a chemical well known for its SiO2 etching ability, along with a silicon precursor to protect SiO2. The ability to selectively etch the Ti HM without impacting key transistor/interconnect components has enabled advanced process technology nodes of today and beyond. This environmentally friendly formulation is now employed in production of advanced high performance microprocessors and produced in a 3000 gallon reactor.
author_names: Nabil George Mistkawi
title: Fundamental Studies in Selective Wet Etching and Corrosion Processes for High Performance Semiconductor Devices
year: 2010

abstract: Specular mode spectroscopic ellipsometry (SE) or reflectometry (SR) from periodic gratings have been successfully demonstrated as accurate methods for extracting detailed topography of integrated circuit structures. However, as critical dimensions become very much less than the current minimum measurement wavelengths and as film thicknesses are simultaneously reduced, there are significant questions regarding the long term usefulness of this method. In this paper, I will attempt to address some major aspects of this problem.
author_names: Fred Lewis Terry
title: Accuracy limitations in specular mode optical topography extraction
venue: SPIE Advanced Lithography
year: 2003