Albert K. Henning

Two-dimensional surface dopant profiling in silicon using scanning Kelvin probe microscopy

A simultaneous combination of scanning Kelvin probe microscopy and scanning atomic force microscopy has been applied to the problem of profiling dopant concentrations in two dimensions in silicon microstructures. By measuring the electrochemical potential difference which minimizes the electrostatic force between probe tip and sample surface, the work‐function difference between the tip and surface is estimated. To the extent that this work‐function difference is a consequence of the dopant concentration at or near the sample surface, doping profiles are inferred from the measurement. Structures examined and presented here include contact holes, and the technologically significant lightly doped drain of a metal–oxide–silicon field‐effect transistor. Using this methodology, one can distinguish relative changes in dopant concentration with lateral resolution less than 100 nm. Sample preparation is minimal, and measurement time is fast compared to other techniques. The measurements have been compared to pred...

Radiation-induced effects in multiprogrammable pacemakers and implantable defibrillators.

Twenty‐three multiprogrammable pacemakers and four implantable cardioverter defibrillators (ICDs) containing either complementary metal‐oxide semiconductor (CMOS) or CMOS/Bipolar integrated circuit (IC) technology were exposed to 6‐MV photon and 18‐MeV electron radiation at various dose levels. Of the 17 pacemakers exposed to photon radiation eight failed before 50 Gy, whereas four of the six pacemakers exposed to electron radiation failed before 70 Gy. Photon scatter doses were well tolerated. For the ICDs detection and charging time increased with accumulated radiation dose, the charging time increased catastrophically at < 50 total pulses delivered when compared with the charging time of six implanted ICDs. Sensitivity and output energy delivered by the ICD pulse were constant during the test. It was found that devices using the shorter channel length IC technology (i.e., 3 p‐m CMOS) were per se harder to ionizing radiation than the devices using larger channel length IC technologies (i.e., either 8 μm CMOS or combined 5 μM CMOS/20 V Bipolar). In fact, none of the devices based on 3 μm CMOS IC technology failed before 76 Gy, which is above the highest dose level (70 Gy) normally used in radiation oncology treatments.

Capacitive effects on quantitative dopant profiling with scanned electrostatic force microscopes

A force‐based scanning Kelvin probe microscope has been applied to the problem of dopant profiling in silicon. Initial data analysis assumed the detected electrostatic force couples the sample and only the tip at the end of a force sensing cantilever. Attempts to compare measurements quantitatively against device structures with this simple model failed. A significant contribution arises from the electrostatic force between the sample and the entire cantilever, which depends strongly upon the relative size of the tip, cantilever, and lateral inhomogeneities in the surface topography and material composition of the sample. Actual and simulated measurements which demonstrate the characteristic signature of this effect are presented.

Imaging integrated circuit dopant profiles with the force‐based scanning Kelvin probe microscope

A force‐based scanning Kelvin probe microscope has been used to image dopant profiles in silicon for integrated circuit devices on a submicron scale. By measuring the potential difference which minimizes the electrostatic force between a probe and surface of a sample, an estimate of the work function difference between the probe and surface may be made. To the extent that this work function difference is a consequence of the dopant concentration near the sample surface, doping profiles are inferred from the measurements. An overview of the measurement technique is presented, along with several examples of resulting dopant imaging of integrated circuits.

Scanning probe microscopy for 2-D semiconductor dopant profiling and device failure analysis

Abstract We have extended the capabilities of an atomic force microscope (AFM) with double heterodyne force detection, to include both electrostatic force microscopy (EFM) and scanning differential capacitance microscopy (SdCM). Samples measured with this tool are imaged simultaneously in each of these three modes. Inhomogeneities in surface topography (AFM), surface work function (EFM) and sub-surface charge (SdCM) are thus detected at once. We work in non-contact mode in order to interact non-destructively with our samples, with resultant lateral spatial resolution of 25–50 nm. Variations in surface topography of less than 1 nm, and surface potential variations as small as 1 mV, are imaged easily. We have applied the techniques based on this tool to microfabricated materials and device structures. In particular, we have studied the metal-oxide-silicon field-effect transistor (MOSFET) structure, of importance to microelectronic science and engineering. Following a brief description of our detection system, this work will describe our measurements of dopant profiles related to this structure. It will also demonstrate our ground-breaking application of scanned probe techniques to the analysis of other materials defects, and of device failure, in these structures. The work will conclude with a quantitative discussion of the three most limiting factors for our techniques: parasitic capacitance; convolved signals; and large-signal behavior of the cantilever.

The Development and Use of Thin Film Thermocouples for Contact Temperature Measurement

A procedure was developed for producing thin film thermocouples (TFTC) on the contact surface of sliding mechanical components. The thermocouple devices were made from thin films of vapor-deposited copper and nickel. The measuring junctions of the thermocouples were approximately 2 μm thick and between 80 μm and 300 μm across. The TFTC devices were found to have extremely rapid (< 1 μS) response to a sudden temperature change and did not significantly disturb the heat flow from the sliding contact. It was found necessary to sandwich the TFTC between thin films of a hard, non-conducting ceramic (Al2O3 in the current work) to insulate the thermocouple electrically from the substrate and protect it during sliding. Thin film thermocouple devices were applied to the measurement of sliding surface temperatures in two cases, oscillatory dry sliding of a polymer pin on a flat surface, and uni-directional dry sliding of a ring over a flat pin surface. Results from the tests verified theoretical predictions. Presen...

Performance of MEMS-based gas distribution and control systems for semiconductor processing

The advent of microelectromechanical systems has enabled dramatic changes in diverse technological areas. In terms of control and distribution of liquids and gases (microfluidics), MEMS-based devices offer opportunities to achieve increased performance, and higher levels of functional integration, at lower cost, with decreased size and increased reliability. This work focuses on recent research and development of high-purity gags distribution and control systems for semiconductor processing. These systems include the following components, based upon both normally-open and normally-closed microvalves: pressure- based mass flow controllers; vacuum leak-rate shut-off valves; and pressure regulators. Advanced packaging techniques enable these components to be integrated into gas sticks and panels which have small size, corrosion-resistant wetted materials, small dead volumes, and minimal particle generation. Principles of operation of components and panels, and performance data at both the component and system level, will be presented. The potential for 10X size reduction (linear dimension), 2X product yield improvement (through increased reliability, improved flow accuracy and repeatability, and contamination reduction), and 5X reduction in process gas consumption, will also be addressed. Particular emphasis on characterization and verification of flow measurements in mass flow controllers (versus NIST standards), and the flow models used in designing and characterizing these systems, will be made.

Out-of-plane microstructures using stress engineering of thin films

A new method is presented to fabricate out-of-plane microstructures using traditional planar micromachining technology. Composite LPCVD polysilicon/silicon nitride beams are fabricated to study this concept. Polysilicon films ranging from 0.5 micrometers to 1.3 micrometers , and silicon nitride films ranging from 150 to 450 nm, were used to fabricate various thickness ratios of composite out-of-plane microstructures. Upon release, these planar structures take on 3D shapes, due to the bending moment caused by inherit internal stresses in the thin films. These stress engineered 3D microstructures (SEMS) open the path to novel microstructures. This paper presents a design theory for SEMS, describes the fabrication process, and discusses the results of initial experiments.

Compact pressure- and structure-based gas flow model for microvalves

The advent of microfluidic systems demands compact models for the description of flow in the constituent system components. The situation is analogous to the evolution of compact models for electron flows in MOSFETs, which were essential for the development of integrated microelectronic systems. We develop here a compact gas flow model for microvalves, which relates valve flow to a limited but meaningful set of parameters. Specifically, these are the gas type; inlet and outlet pressures; ambient temperature; valve inlet diameter; the gap between the membrane and the valve inlet; and the coefficient of discharge of the valve inlet. The result is a simple, accurate model, appropriate for the design and analysis of microfluidic systems. We also demonstrate a characterization methodology for extracting the required model parameters from measurements of flow versus pressure and gap. This characterization has produced values for the coefficient of discharge, which match expectations based on previous theory and measurement. It has also produced a single parameter describing the effect of the gap in controlling the flow, across broad ranges of valve inlet diameter, membrane-to-inlet gap, and pressure.

Factors affecting silicon membrane burst strength

Factors affecting the fracture strength of single-crystal silicon membranes are assessed. These factors include: membrane shape at the membrane’s intersection with structural frames or sidewalls, membrane thickness, membrane surface roughness, membrane mis-orientation to the principal crystallographic axes, wafer starting material quality, membrane stress (or pre-tension), and microstructure and shape at bond interfaces, such as the anodic bond interface between membrane and Pyrex wafers. Measurements of fracture strength versus these factors are made. Direct measurements of stress are also made using micro-Raman techniques. Simulations of membrane structures are studied, in order to evaluate the measurements. The results indicate that the predominant factor affecting fracture strength is surface roughness.