Specific Process Knowledge/Characterization/Sample imaging: Difference between revisions

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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).  

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==Comparison of optical microscope, optical profiler, SEM, AFM and stylus profiler for sample imaging==

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![[Specific_Process_Knowledge/Characterization/Optical_microscope|Optical microscopes]]

![[Specific_Process_Knowledge/Characterization/SEM:_Scanning_Electron_Microscopy|SEM]]

![[Specific_Process_Knowledge/Characterization/AFM:_Atomic_Force_Microscopy|AFM]]

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!Generel description

|Optical microscope  

[[Specific_Process_Knowledge/Characterization/SEM_Supra_2| SEM Supra 2]],  

[[Specific_Process_Knowledge/Characterization/SEM_Supra_3| SEM Supra 3]],  

[[Specific_Process_Knowledge/Characterization/SEM_Tabletop_1| SEM Tabletop 1]])

(NanoMan)

|Stylus profiler  

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!Operation priciple

|Light

|Light

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*Secondary electrons

*Backscattered electrons

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!Sample information

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*Film thickness

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|3D surface topography

|3D surface topography (if you make a map scan)

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!Vertical resolution

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*PSI: 0.01 nm

*VSI: 1 nm

Depends on what SEM you use

|< 1Å  

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!Horizontal resolution

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*10x objective: 4.95 &mu;m  

*100x objective: 0.495 &mu;m

Depends on what SEM you use

|Down to 1.4 nm

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!Resolution limitations

|Objectives and wavelength of light

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!Magnification

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!XY range/field of view

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!Z range

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!Working distance

|Few mm

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!Sampling speed

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!Sample requirements  

|None

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|Samples have to be (semi)conducting, but may have a thin (> ~ 5 µm) layers of non-conducting materials on top.

|Sample dimensions have to be smaller than stylus dimensions

|Sample dimensions have to be smaller than tip dimensions

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!Batch size

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*One 100 mm wafer  

*One 150 mm wafer  

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*One small sample

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!'''Allowed materials'''

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*All sample materials, expect:  

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*All standard cleanroom materials, except samples that might damage or stick to the tip.

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There is a lot of [[Specific Process Knowledge/Characterization/Optical microscope|optical microscopes]] scattered around in the cleanroom because they are in great need. They are useful if, for instance, you need to

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.

The main purpose is 3D topographic imaging of surfaces, Step height measurements in smaller trenches/holes than can be obtained with standard stylus method, roughness measurements with larger FOV than the AFM, but less horisontal resolution.

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:

* Hardware: In order to work the SEM needs a chamber under 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.

The [[Specific Process Knowledge/Characterization/AFM: Atomic Force Microscopy|atomic force microscope]] has limited use as a sample imaging instrument. In some cases the resolution of the SEM is not enough: