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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 strucutures 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.
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 strucutures 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.


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. Another SEM advantage is the stage that allows you to image your sample from almost any angle. The SEM is, however, much more complicated in terms of  
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 milimeters.
* Much better resolution: Down to a few nanometers.
* Much higher magnifications possible: Up to 500.000 times on some samples.
* The stage: It allows you to image your sample from almost any angle.  
* Tunability: One can tune the image in a number of ways in order to enhance topography or material contrast
 
The SEM is, however, much more complicated in terms of  
* Operation: You need training and it takes some experience and skill to obtain good images.
* Operation: You need training and it takes some experience and skill to obtain good images.
* Hardware: In order to work the SEM needs vacuum and sophisticated electronics.
* Hardware: In order to work the SEM needs vacuum and sophisticated electronics.
* Sample preparation and mounting: You may have to prep your sample in several ways, either coating, cleaving or mounting on specific sample holders.
* Sample preparation and mounting: You may have to prep your sample in several ways, either coating, cleaving or mounting on specific sample holders.
   
 
The image that one gets from a SEM  


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