Patent Application
20120223227
1. Field of the Invention
The present invention relates to methods and apparatus for electron beam imaging and for processing electron beam image data.
2. Description of the Background Art
The scanning electron microscope (SEM) is a type of electron microscope. In an SEM, the specimen is scanned with a focused beam of electrons which produce secondary and/or backscattered electrons (SE and/or BSE) as the beam hits the specimen. These are detected and typically converted into an image of the surface of the specimen. The image is typically from a “normal” view (i.e. a view from a perspective perpendicular to the semiconductor surface).
However, in recent years, the structure and morphology of critical structures and defects in integrated circuits has become increasingly important. The advent of device structures that are constructed vertically above the semiconductor surface may need to be visualized in order to understand how the process is performing. Critical defects within the semiconductor device are increasingly more subtle, from an absolute perspective, and require additional contextual information to affect root cause analysis.
One embodiment relates to a method of real-time three-dimensional electron beam imaging of a substrate surface. A primary electron beam is scanned over the substrate surface causing electrons to be emitted therefrom. The emitted electrons are simultaneously detection using a plurality of at least two off-axis sensors so as to generate a plurality of image data frames, each image data frame being due to electrons emitted from the substrate surface at a different view angle. The plurality of image data frames are automatically processed to generate a three-dimensional representation of the substrate surface. Multiple views of the three-dimensional representation are then displayed.
Another embodiment relates to an apparatus configured for real-time three-dimensional electron beam imaging of a substrate surface. The apparatus includes at least a source for generating a primary electron beam, scan deflectors, a detection system, and an image data processing system. The scan detectors are configured to deflect the primary electron beam so as to scan the primary electron beam over the substrate surface causing electrons to be emitted from the substrate surface. The detection system is configured for the simultaneous detection of emitted electrons using a plurality of at least two off-axis sensors so as to generate a plurality of image data frames. Each image data frame is due to electrons emitted from the substrate surface at a different view angle. The image data processing system is configured to automatically process the plurality of image data frames to generate multiple views of a three-dimensional representation of the substrate surface.
Other embodiments, aspects and features are also disclosed.
Scanning electron microscope (SEM) imaging and viewing of critical locations of semiconductor wafers are commonly taken from a “normal” view. However, from such a normal view, it is difficult to perceive topological information of the sample surface.
Previous techniques for obtaining SEM images with non-normal angular perspectives typically involve manually tilting of either the SEM column or the sample to change the angle of the incident beam relative to the sample surface. Another previous technique involves sequentially acquiring two images at two different non-normal angular view points. After the acquisition of the second image, a user may then utilize a stereoscopic viewing device to perceive a three-dimensional image of the sample surface.
However, these previous techniques require mechanical movement (of either the column or sample stage) and the sequential acquisition of two images. These requirements adversely impact the throughput of an e-beam inspection tool. Moreover, the viewing perspective is limited based on the tilt angle(s) used during image acquisition.
The apparatus and methods disclosed herein provide real-time three-dimensional topology and context information about critical structures and defects during a semiconductor manufacturing process. This enables single-pass visualization and more complete characterization of defects in high-k dielectric metal gate transistors and other three-dimensional structures. Using the techniques disclosed herein, an order of magnitude savings may be achieved in the time required to obtain three-dimensional imaging of large quantities of critical regions of interest of semiconductor samples. Precise position and imaging collection of a critical area is provided, allowing a more complete understanding of the structure of interest in the context of the background pattern and the constituent materials, thus achieving better absolute sensitivity.
Referring to
As shown in
As a result of the scanning of the primary beam 202, electrons are emitted or scattered from the sample surface. These emitted electrons may include secondary electrons (SE) and/or backscattered electrons (BSE). The emitted electrons are then extracted from the wafer or other sample (wafer/sample) 210. These emitted electrons are exposed to the action of the final (objective) lens by way of the electromagnetic field 208. The electromagnetic field 208 acts to confine the emitted electrons to within a relatively small distance from the primary beam optic axis and to accelerate these electrons up into the column. In this way, a scattered electron beam 212 is formed from the emitted electrons. The Wien filter 204 deflects the scattered electron beam 212 from the optic axis of the primary beam 202 to a detection axis (the optic axis for the detection system of the apparatus). This serves to separate the scattered electron beam 212 from the primary beam 202.
In accordance with one embodiment of the invention, the detection system may include, for example, a segmented detector 300, which is shown in further detail in
As shown in
Referring to
As depicted in
In this below-the-lens configuration 400, the off-axis or “side” sensors or detector segments (408-1, 408-2, 408-3, and 408-4) are positioned below the objective lens 402 at the bottom of the electron beam column (near the target substrate). Under certain conditions, electrons emitted at higher polar angles (preferably 45 degrees or more) relative to the surface normal (i.e. emitted with trajectories closer to the surface) will preferentially reach such below-the-lens detectors. The detectors may be separated or joined together to form a segmented detector. As these electrons are typically more sensitive to surface topology, images formed with such detectors show the topography of the surface with an azimuthal perspective defined by the detector positioning with respect to the primary beam optic axis and the sample/wafer plane.
In the cross-sectional diagram of
Referring to
As depicted in
In this behind-the-lens configuration 500, the off-axis or “side” sensors or detector segments (508-1, 508-2, 508-3, and 508-4) are on the opposite side of the objective lens 502 from the target substrate 504. In other words, the objective lens 502 is between the target substrate 504 and the “side” detectors or detector segments (508-1, 508-2, 508-3, and 508-4). In this case, the magnetic field of the objective lens may be configured to confine the emitted electrons (which may include electrons emitted at polar angles greater than 45 degrees from the surface normal) and direct them towards the behind-the-lens detector array (508-1, 508-2, 508-3, and 508-4). Similarly to the below-the-lens configuration 400, images may be formed using the detected signals from the behind-the-lens configuration 500 that show topographical information about the surface of the target substrate 504.
In the cross-sectional diagram of
In both the second embodiment 400 or third embodiment 500 described above, more or fewer detector segments may be used. For example, if three evenly-spaced detector segments are used, then each may provide a view angle effectively spaced 120 degrees apart in azimuthal angle. As another example, if five evenly-spaced detector segments are used, then each may provide a view angle effectively spaced 72 degrees apart in azimuthal angle. As another example, if six evenly-spaced detector segments are used, then each may provide a view angle effectively spaced 60 degrees apart in azimuthal angle. Also, the detector segments or separate detectors may be discrete so as to collect scattered electrons from much smaller ranges of azimuthal angles. Furthermore, in addition to the “side” (non-normal view) detectors, a conventional detector configuration (such as the central detector 302 in
Referring back to
Design and material data 108 relating to the integrated circuit being fabricated on the semiconductor surface may be accessed during the automatic processing 106. The three-dimensional representation may then be aligned 109 to the design data. Subsequently, a surface height map from the three-dimensional representation may be rectified 110 using the layer information in the design data. Alternatively, the surface height map from the three-dimensional representation may be calibrated 111 using image data from a standard sample, as may be appreciated by one of skill in the pertinent art.
In accordance with one embodiment, images corresponding to left-eye and right-eye stereoscopic views may be generated 112 using the three-dimensional representation. Example of left-eye and right-eye stereoscopic views of a region of interest are shown in
In accordance with another embodiment, an exemplary “aerial flyover” view path may be determined 122. The view path preferably views the region of interest from a range of angles and distances. A video comprising a sequential set of frames is then generated 124 based on the view path. The frames of the video depict perspective views as if a camera was “flying over” the region of interest. In other words, a video of the region of interest is generated 124 as the angle, and/or tilt and/or zoom of the view may be varied smoothly. Optionally, a texture map based on the material data may be aligned and overlaid 114 on top of each frame to show material contrast. Four example video frames captured from a video are provided in
In accordance with another embodiment, an image of a perspective view of the three-dimensional representation may be generated 128. Optionally, a texture map based on the material data may be aligned and overlaid 114 on top of the image to show material contrast. Thereafter, the perspective view may be displayed 130 to the user via a wireless-connected tablet computer or other computer display. The display may be in real time while the target substrate is still under the scanning electron beam. Interaction with the 3D representation may be provided by way of motion sensitive controls, for example, on a motion-sensitive touch screen of the tablet computer. User input may be received 132 by way of the motion sensitive controls, and the perspective of the stereoscopic view may be adjusted 134 based on the user input. For example, tilt, rotation and zoom inputs may be used to change the perspective displayed.
In the above description, numerous specific details are given to provide a thorough understanding of embodiments of the invention. However, the above description of illustrated embodiments of the invention is not intended to be exhaustive or to limit the invention to the precise forms disclosed. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific details, or with other methods, components, etc. In other instances, well-known structures or operations are not shown or described in detail to avoid obscuring aspects of the invention. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.
These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims. Rather, the scope of the invention is to be determined by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.
