Neal T. Sullivan

Investigation of the effects of charging in SEM-based CD metrology

Scanning electron microscopes are considered the most likely tool for future CD metrology down to 0.1 micron linewidths and below. Charging effects on insulating materials are a long standing problem for electron microscopes. The shrinking design rules are making the measurement errors caused by charging more significant. In this paper a model is proposed which incorporates charging effects into a Monte Carlo simulation model. The model stems from the notion of beam induced conductivity, an established phenomenon whereby an insulator becomes conducting for a brief period of time after being hit by a primary electron. The insulator becomes conducting only within the interaction volume of the primary electron. So after multiple scans of the primary beam has occurred, it can be expected that because of the transient beam induced conductivity that the resulting charge distribution will be such a to create an equipotential surface where significant primary beam dose has occurred. This concept is applied to resist by treating the top region of the resist as a negatively charged potentials. The substrate is given a different potential In general different materials can be expected to have different potentials. One important consequence is that the corners of the resist line, if they are sharp, have strong electric fields and they repel the beam electron. We calculate the electrostatic fields given the resist geometry,then we calculate the beam deflection caused by this field, we remap Monte Carlo simulation data to fold in this effect, and finally we compare with some experimental data to see if this charging effect can account for the apparent resolution degradation that occurs at the edges of resist lines with scanning electron microscopes.

Novel fast neutron counting technology for efficient detection of special nuclear materials

Results from a fully independent thin film process for manufacturing non-lead glass Microchannel plate (MCP) detectors using nano-engineered thin films for both the resistive and emissive layers are presented. These novel MCP devices show high gain, less gain degradation with extracted charge, and greater pore to pore and plate to plate uniformity than has been possible with conventional lead glass structures. Extension of MCP to plastic substrates, for the purpose of fast neutron detection is disclosed and preliminary MCP functionality results are presented. Simulation results, predicting fast neutron detection performance for the plastic MCP device are presented and discussed

Toward a unified advanced CD-SEM specification for sub-0.18-μm technology

The stringent critical dimension control requirements in cutting edge device facilities have placed significant demands on metrologists and upon the tools they use. We are developing a unified, advanced critical dimension scanning electron microscope specification in the interests of providing a unified criterion of performance and testing. The specification is grounded on standard definitions and strong principles of metrology. The current revision is to be published as a SEMATECH document. A new revision, now in progress, will embody the consensus of a vendor/user conference.

Development of atomic layer deposition-activated microchannel plates for single particle detection at cryogenic temperatures

Atomic layer deposition (ALD) technology is used to nanoengineer functional films inside the pores of microchannel plate (MCP) electron multipliers, enabling a novel MCP manufacturing technology that substantially improves performance and opens novel applications. The authors have developed custom tools and recipes for the growth of conformal films, with optimized conductance and secondary electron emission inside very long channels (∼6–20 μm diameter and >600 μm length, with tens of millions of channels per single MCP) by ALD. The unique ability to tune the characteristics of these ALD films enables their optimization to applications where time-resolved single particle imaging can be performed in extreme conditions, such as high counting rates at cryogenic temperatures. Adhesion of the conductive and emissive nanofilms to the 20 μm pore MCP glass substrates and their mechanical stability over a very wide range of temperatures (10–700 K) were confirmed experimentally. Resistance of ALD MCPs was reproducible during multiple cool-down cycles with no film degradation observed. Optimizing resistance of novel MCPs for operation at cryogenic temperature should enable high count rate event detection at temperatures below 20 K.

CD-SEM-based critical shape metrology of integrated circuits

With critical dimensions (CD) of integrated circuits shrinking to tens of nanometers, accurate metrology of three-dimensional feature shapes at different stages of the lithographic process becomes crucial to circuit performance. We propose Critical Shape Metrology (CSM), a CD-SEM-based technique that extracts accurate feature shape information from images obtained during routine in-line wafer inspection. Intensity profiles from CD-SEM images of known materials are compared in real time to profiles in an off-line generated Monte-Carlo SEM simulation library for the same materials with various model shapes. When the best match is found, metrics like bottom CD, top CD, sidewall angle, foot size and angle, and corner rounding can be obtained with high accuracy. The proposed technique takes advantage of the high resolution and throughput of low-voltage CD-SEMs, and does not require any additional tool calibration beyond the standard calibrations performed for conventional top-down CD metrology. While similar to optical scatterometry in concept, this technique allows for measurement of both isolated targets and dense arrays. Examples of performance on etched polysilicon and resist lines of different shapes are included and compared to SEM cross-sections and CD-AFM data.

Improving detection efficiency in a cryogenic environment - implications for DESIREE

The high electrical resistance of a microchannel plate at cryogenic temperatures presents a severe limitation on the detection count rate at low temperatures. We are currently investigating the detector properties of a novel atomic layer deposition activated MCP developed by Gorelikov et al [1]. This is of particular interest to us as MCPs are used for particle detection at the cryogenic DESIREE facility at Stockholm University.