Gian Lorusso

Sub-50-nm isolated line and trench width artifacts for CD metrology

We present a technique to produce isolated lines and trenches with arbitrary widths in the range of 12 nm to 500 nm, arbitrary heights and depths in the range of 100 nm to 2 μm, 90-degree sidewall angle, and top corner radii as small as 5 nm. These structures are ideal candidates as Critical Dimension (CD) absolute standards. The sidewall angle can further be varied to create an arbitrary sidewall angle that can be accurately measured.

Three-dimensional simulation of top down scanning electron microscopy images

Low voltage scanning electron microscopy (SEM) metrology and inspection are performed by immersing the sample in an electric field; under this condition, when a scanning electron beam images a sample containing insulating features (like oxides and resist), a surface global charge builds up to offset the applied field and a transverse local field will form as a result of the scanning beam. The surface global charge is responsible for the voltage contrast and imaging properties, while local fields degrade image resolution. In this article we describe a simulation approach able to explain the imaging properties of charged surfaces and how resolution is affected by local fields. Using electron ray tracing in the column, the simulation follows both the emitted and primary electron trajectories outside the sample. In addition, Monte Carlo scattering simulation calculates the electron trajectory and charge deposition inside the sample. The resulting charge density is used to calculate the field inside and outsid...

Three dimensional simulations of SEM imaging and charging

SEM based CD control and wafer inspection has an increasingly active role in the semiconductor industry. Current design rules require a CD control with a precision in the nanometer range. In order to achieve this precision, a complete model of the image formation mechanism is desirable. For this reason we present a three-dimensional simulation of scanning electron microscope (SEM) images. The simulations include Monte Carlo electron scattering, charging in the substrate and electron ray-tracing in the column. We investigate some specific cases in CD-SEM metrology: We will describe the effect of scan orientation relative to the orientation of the imaged feature on the apparent beam width (ABW), the effect of magnification on contact imaging, and the effect of residue in resist trenches. Our results, regarding these examples, clearly indicate that a fully three-dimensional numerical simulation is needed to obtain an understanding of image formation and resolution limiting factors.

SEM voltage contrast simulations

High resolution inspection and metrology is an important part of current semiconductor technology and has an increasingly active role as miniaturization is pushed beyond 200 nm. Current and future semiconductor design rules require not only high resolution CD control and inspection but also the ability to image high aspect ratio structures patterned on complex layers. This goal is usually achieved by using e-beam based tools that exploit voltage contrast to form images of deep structures; although useful, such images are not obviously and uniquely determined by their topographical counterpart since other parameters may significantly affect image appearance. In this paper we present a simulation approach that explains the imaging properties of charged surfaces under different conditions. This approach shows that in order to get a physical description of an e-beam image formation process, the surface must be considered as an electrostatic optical element with its own properties.

Automated CD SEM tilt-ready for primetime: a fast in-line methodology for differentiating lines vs. spaces

One of many challenges the process or metrology engineers face is incorrect flagging on the process control chart. It could either be a result of an un-optimized recipe that measures the wrong feature (a space instead of line) or a feature placement error due to tool limitation. This can be a costly problem in the fab where processes are put on hold, feedback loops are corrupted and backlogs are built up unnecessarily. Often many hours must be spent by operators re-inspecting lots and process or metrology engineers re-qualifying the recipes. Most CD SEMs use algorithms employing pattern matching and contrast difference to differentiate between line and space. However, the shrinking node requirement, limited contrast between line and space images and the 1:1 line and space ratios have revealed limitations of these algorithms. Recently, a metrology solution using beam tilt on the KLA-Tencor ECD-2 has been developed to tackle the problem of dense line or dense trench array measurements. This methodology is a line vs. space detection mechanism that precedes the metrology measurement. This application is quick and oblivious to low contrast differences between line/space and to systematic errors that occur with narrow feature positioning. Whether or not the specified feature type for measurement is centered in the field of view, it always detects the requested feature type and sets the metrology measurement to be made accordingly and therefore significantly reducing false negatives and false positives. This application also allows for greater tolerance in recipe setup and placement error, and thus lightens the burden of recipe creation on the novice user. This technique can also be incorporated into waferless design based metrology where limited prior knowledge of the wafer is one of the requirements. Future potential of this metrology solution will also be discussed. This could include detecting undercut situations and possibly even correcting bottom CD based on undercut angular detection.