Specific Process Knowledge/Characterization/Sample imaging: Difference between revisions
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== Sample imaging == | == Sample imaging == | ||
In the cleanroom at DTU Nanolab a number of instruments are available for sample imaging, including several optical microscopes, and optical profiler, a number of SEMs (scanning electron microscopes), an AFM (atomic force microscope) and two stylus profilers (Dektak). | |||
The optical microscopes provide fast and easy information about most samples without sample preparation. The resolution is limited by the objectives and | The optical microscopes provide fast and easy information about most samples without sample preparation. The resolution is limited by the objectives and wavelength of the light. Also the depth of focus is limited, especially for higher magnifications. | ||
The main purpose of the optical profiler is to obtain 3D images of different samples and to measure surface roughness or step heights, also for structures with high aspect ratio. Two different types of measurements can be done - confocal and interference (phase shift and vertical scanning interference) measurements. It is possible to measurement | The main purpose of the optical profiler is to obtain 3D images of different samples and to measure surface roughness or step heights, also for structures with high aspect ratio. Two different types of measurements can be done - confocal and interference (phase shift and vertical scanning interference) measurements. It is possible to measurement height aspect ratio structures. The resolution is limited by the objectives and the pixel size on the screen. | ||
The SEMs are used for inspection of different sample. The resolution is very good - It is possible to obtaion good images of structures smaller then 100 nm with all SEMs in the cleanroom. Samples can be either flat or tilted. | The SEMs are used for inspection of different sample. The resolution is very good - It is possible to obtaion good images of structures smaller then 100 nm with all SEMs in the cleanroom. Samples can be either flat or tilted. | ||
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!Sample information | !Sample information | ||
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|3D surface | |3D surface topography | ||
*Step height | *Step height | ||
*Surface roughness | *Surface roughness | ||
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|-style="background:LightGrey; color:black" | |-style="background:LightGrey; color:black" | ||
!Resolution limitations | !Resolution limitations | ||
|Objectives and | |Objectives and wavelength of light | ||
|Objectives and pixel size on the screen | |Objectives and pixel size on the screen | ||
|Interaction volume | |Interaction volume | ||
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!'''Allowed materials''' | !'''Allowed materials''' | ||
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*All standard cleanroom materials (optical | *All standard cleanroom materials (optical measurement) | ||
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*All standard cleanroom materials (optical measurement) | *All standard cleanroom materials (optical measurement) | ||
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Using the different options such as bright/dark field, polarizer or transmitted/reflected light one can find a better signal for a specific need. Some of them have a camera that allows you to capture and store images. | Using the different options such as bright/dark field, polarizer or transmitted/reflected light one can find a better signal for a specific need. Some of them have a camera that allows you to capture and store images. | ||
One of the advantages of the optical microscopes is that they provide fast and easy accessible information about any sample without any kind of sample preparation. They do, however, also have some limitations. Since the depth of focus is quite limited, especially at high magnifications, one will experience problems when trying to image | One of the advantages of the optical microscopes is that they provide fast and easy accessible information about any sample without any kind of sample preparation. They do, however, also have some limitations. Since the depth of focus is quite limited, especially at high magnifications, one will experience problems when trying to image structures that have been etched more than some 10 µm: One cannot focus on both the top and the bottom at the same time. Another disadvantage is the physical limit to the resolution that makes it impossible to image structures below 1 µm. | ||
=== [[Specific Process Knowledge/Characterization/Profiler#Optical_Profiler_(Sensofar)|The optical profiler (Sensofar)]] === | === [[Specific Process Knowledge/Characterization/Profiler#Optical_Profiler_(Sensofar)|The optical profiler (Sensofar)]] === | ||
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Both shortcomings of the optical microscopes mentioned above are addressed by the use of a beam of electrons (as you do in a SEM) instead of light. The depth of focus and the resolution of a [[Specific Process Knowledge/Characterization/SEM: Scanning Electron Microscopy|scanning electron microscope]] are at least one order of magnitude better. The list of advantages of a SEM compared to an optical microscope includes: | Both shortcomings of the optical microscopes mentioned above are addressed by the use of a beam of electrons (as you do in a SEM) instead of light. The depth of focus and the resolution of a [[Specific Process Knowledge/Characterization/SEM: Scanning Electron Microscopy|scanning electron microscope]] are at least one order of magnitude better. The list of advantages of a SEM compared to an optical microscope includes: | ||
* Much better depth of focus: Depending on the image setup it may be on the order of | * Much better depth of focus: Depending on the image setup it may be on the order of millimeters. | ||
* Much better resolution: Down to a few nanometers. | * Much better resolution: Down to a few nanometers. | ||
* Much higher magnifications possible: Up to 500.000 times on some samples. | * Much higher magnifications possible: Up to 500.000 times on some samples. | ||