Specific Process Knowledge/Characterization/Measurement of film thickness and optical constants: Difference between revisions
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== Measurement of Film Thickness and Optical Constants == | == Measurement of Film Thickness and Optical Constants == | ||
Thickness measurement of thin films can be done by optical measurement methods. | Thickness measurement of thin films can be done by optical measurement methods. We have various techniques for this: Ellipsometry (with the Ellipsometer VASE) and reflectivity measurements (with the FilmTek or optical profilers) or X-ray diffractometer. | ||
Measurement if the optical constants of a thin film is measured together with the thickness of the film | If the thin film is not transparent to light or there is insufficient reflectance at the interfaces in your sample, you must find another way to measure the thickness. You can for instance etch a pattern down to the next layer or substrate and then measure the etch step by profilometry. Or if you deposit a layer by PVD you may be able to physically mask part of your sample or an adjacent dummy sample to create a sharp step that can be measured by profilometry (etching will usually create a sharper step, but a physical mask can give you a quick-and-dirty estimate). Another option not described further on this page is to cleave the sample to create a chip whose cross-section can be imaged in [[Specific Process Knowledge/Characterization/SEM: Scanning Electron Microscopy|an SEM]] . | ||
Measurement if the optical constants of a thin film is measured together with the thickness of the film either by ellipsometry or by refraction (using the FilmTek). Some of these methods also allow you to indirectly determine, e.g., the surface roughness of the layers in your sample, or, by X-ray reflectivity, the density of the layers. | |||
<br clear="all" /> | <br clear="all" /> | ||
==Comparison of the different | ==Comparison of the different methods== | ||
{|border="1" cellspacing="1" cellpadding="3" style="text-align:left;" | {|border="1" cellspacing="1" cellpadding="3" style="text-align:left;" | ||
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![[Specific Process Knowledge/Characterization/Optical characterization#Filmtek_4000|FilmTek 4000]] | ![[Specific Process Knowledge/Characterization/Optical characterization#Filmtek_4000|FilmTek 4000]] | ||
![[Specific Process Knowledge/Characterization/Optical characterization#Ellipsometer|Ellipsometer]] | ![[Specific Process Knowledge/Characterization/Optical characterization#Ellipsometer|Ellipsometer]] | ||
![[Specific Process Knowledge/Characterization/Optical | ![[Specific Process Knowledge/Characterization/Profiler|Optical Profiler]] | ||
![[ | ![[Specific_Process_Knowledge/Characterization/XRD/Process_Info#XRR|XRD SmartLab]] | ||
![[ | ![[Specific Process Knowledge/Characterization/Profiler|Etch/mask + stylus method]] | ||
|- | |- | ||
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!Generel description | !Generel description | ||
|Thin films up to 250 µm, Especially good for thick thin films and for wafer mapping | |Thin films up to 250 µm, Especially good for thick thin films and for wafer mapping | ||
|Good for very thin films down to a few Å | |Good for very thin films down to a few Å | ||
|Thin films up to 20µm, especially good for measuring in a small point (down to 4µm) | |Thin films up to 20µm, especially good for measuring in a small point (down to 4µm) | ||
|Good for very thin films down to a few Å | |||
|Technique for thickness measurement for non-transparent films | |Technique for thickness measurement for non-transparent films | ||
|- | |- | ||
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|Reflection | |Reflection | ||
|Ellipsometry | |Ellipsometry | ||
|Reflection | |Reflection | ||
|Etch combined with stylus profiling | |X-ray reflection | ||
|Etch or physical mask combined with stylus profiling | |||
|- | |- | ||
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|-style="background:WhiteSmoke; color:black" | |-style="background:WhiteSmoke; color:black" | ||
!Film thickness range | !Film thickness range | ||
|<250 µm (for silicon oxides > ~75nm) | |<250 µm (for silicon oxides > ~75nm, thinner layer can be measured using the UV light source) | ||
|20 Å to ~ | |20 Å to ~10 µm (for silicon oxide) | ||
|~ | |~30 nm-20 µm (down to 10nm when using the base without the microscope) | ||
|few nm to approx. 100 nm (up to 300 nm for low Z materials) | |||
|~ | |~100 nm to 1 mm | ||
|- | |- | ||
|-style="background:LightGrey; color:black" | |-style="background:LightGrey; color:black" | ||
!Film thickness accuracy | !Film thickness accuracy | ||
|Very dependent of how good the model fits (if the fit is good it could be within 1% for a single layer) | |Very dependent of how good the model fits (if the fit is good it could be within 1 % for a single layer) | ||
|Very dependent of how good the model fits. | |Very dependent of how good the model fits. | ||
|Very dependent of how good the model fits.(Not so good fitting possibility) | |||
|Very dependent of how good the model fits.(Not so good fitting | |Very good, depends on the model fit | ||
|Depends on | |Depends on end-stop accuracy (of the etch) or step sharpness (if a physical deposition mask is used) | ||
|- | |- | ||
|-style="background:WhiteSmoke; color:black" | |-style="background:WhiteSmoke; color:black" | ||
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|not any limits | |not any limits | ||
|not any limits | |not any limits | ||
|not any limit | |not any limit | ||
|No index measurement | |||
|No index measurement | |No index measurement | ||
|- | |- | ||
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|not known | |not known | ||
|not known | |not known | ||
|not know | |not know | ||
|not relevant | |||
|not relevant | |not relevant | ||
|- | |- | ||
|-style="background:WhiteSmoke; color:black" | |-style="background:WhiteSmoke; color:black" | ||
!Wavelength range | !Wavelength range | ||
|400-1000 nm | |400-1000 nm (with UV source down to 250nm) | ||
|210-1690 nm | |210-1690 nm | ||
|350-950 nm | |350-950 nm | ||
|Cu K<sub>α</sub> radiation (1.5406 Å) | |||
|Not relevant | |Not relevant | ||
|- | |- | ||
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*SU8 | *SU8 | ||
*Other polymers | *Other polymers | ||
*Very thin layers of metals | *Very thin layers of metals | ||
*and many more | *and many more | ||
|Any film that is transparent to the light in the given wavelength range | |Any film that is transparent to the light in the given wavelength range | ||
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*Very thin layers of metals (<20 nm) | *Very thin layers of metals (<20 nm) | ||
*and many more | *and many more | ||
|In principle any film that is transparent to the light in the given wavelength range. It is limited by the refractive index files in the software and only one model (Cauchy) | |In principle any film that is transparent to the light in the given wavelength range. It is limited by the refractive index files in the software and only one model (Cauchy) | ||
ex: | ex: | ||
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*Very thin layers of metals (<20 nm) | *Very thin layers of metals (<20 nm) | ||
*and many more | *and many more | ||
|Any film that is transparent to the X-rays | |||
including thin layers of metals directly on Si wafers | |||
| | | | ||
* | *Any that can be etched and stopped without overetching in the underlying material or any material deposited with PVD and partly physically masked. | ||
|- | |- | ||
|-style="background:WhiteSmoke; color:black" | |-style="background:WhiteSmoke; color:black" | ||
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*larger samples might also be possible, please ask | *larger samples might also be possible, please ask | ||
| | | | ||
*small samples ( | *small samples (smallest spotsize 125µm) | ||
*50 mm wafers | *50 mm wafers | ||
*100 mm wafers | *100 mm wafers | ||
*150 mm wafers (any sample size below 150mmx150mm | *150 mm wafers (any sample size below 150mmx150mm | ||
*larger samples might also be possible, please ask | *larger samples might also be possible, please ask | ||
| | | | ||
*small samples (at least 3mmx3mm) | *small samples (at least 3mmx3mm) | ||
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*150 mm wafers (any sample size below 150mmx150mm | *150 mm wafers (any sample size below 150mmx150mm | ||
*larger samples might also be possible, please ask | *larger samples might also be possible, please ask | ||
|Limited by the etching method and the stylus | | | ||
*up to 150 mm wafers (less signal if the sample is smaller than ~1x1 cm) | |||
|Limited by the etching method and the stylus profiling instrument. | |||
|- | |- | ||
|-style="background:LightGrey; color:black" | |-style="background:LightGrey; color:black" | ||
!'''Allowed materials''' | !'''Allowed materials''' | ||
| | | | ||
*All materials - some | *All materials - some need a carrier - see the manual for instructions | ||
| | | | ||
*All materials | *All materials | ||
| | | | ||
*All materials | *All materials | ||
| | | | ||
*Any material that can/may be etched and allowed that chosen etch equipment/bath | *All materials | ||
| | |||
*Any material that can/may be etched and allowed that chosen etch equipment/bath or that can be deposited by PVD using a physical mask | |||
|- | |||
|-style="background:LightGrey; color:black" | |||
!'''Comments''' | |||
| | |||
| | |||
If no model exists for your layer structure, developing a model may require some work. The instrument has many models available already. | |||
| | |||
| | |||
Measurement and analysis quite time consuming. Can determine layer roughness and density including density gradients | |||
| | |||
Direct measurement. | |||
|- | |- | ||
|} | |} | ||
<br clear="all" /> | <br clear="all" /> | ||
Latest revision as of 13:36, 22 January 2024
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Unless otherwise stated, this page is written by DTU Nanolab internal
Measurement of Film Thickness and Optical Constants
Thickness measurement of thin films can be done by optical measurement methods. We have various techniques for this: Ellipsometry (with the Ellipsometer VASE) and reflectivity measurements (with the FilmTek or optical profilers) or X-ray diffractometer.
If the thin film is not transparent to light or there is insufficient reflectance at the interfaces in your sample, you must find another way to measure the thickness. You can for instance etch a pattern down to the next layer or substrate and then measure the etch step by profilometry. Or if you deposit a layer by PVD you may be able to physically mask part of your sample or an adjacent dummy sample to create a sharp step that can be measured by profilometry (etching will usually create a sharper step, but a physical mask can give you a quick-and-dirty estimate). Another option not described further on this page is to cleave the sample to create a chip whose cross-section can be imaged in an SEM .
Measurement if the optical constants of a thin film is measured together with the thickness of the film either by ellipsometry or by refraction (using the FilmTek). Some of these methods also allow you to indirectly determine, e.g., the surface roughness of the layers in your sample, or, by X-ray reflectivity, the density of the layers.
Comparison of the different methods
FilmTek 4000 | Ellipsometer | Optical Profiler | XRD SmartLab | Etch/mask + stylus method | |
---|---|---|---|---|---|
Generel description | Thin films up to 250 µm, Especially good for thick thin films and for wafer mapping | Good for very thin films down to a few Å | Thin films up to 20µm, especially good for measuring in a small point (down to 4µm) | Good for very thin films down to a few Å | Technique for thickness measurement for non-transparent films |
Method | Reflection | Ellipsometry | Reflection | X-ray reflection | Etch or physical mask combined with stylus profiling |
Film thickness range | <250 µm (for silicon oxides > ~75nm, thinner layer can be measured using the UV light source) | 20 Å to ~10 µm (for silicon oxide) | ~30 nm-20 µm (down to 10nm when using the base without the microscope) | few nm to approx. 100 nm (up to 300 nm for low Z materials) | ~100 nm to 1 mm |
Film thickness accuracy | Very dependent of how good the model fits (if the fit is good it could be within 1 % for a single layer) | Very dependent of how good the model fits. | Very dependent of how good the model fits.(Not so good fitting possibility) | Very good, depends on the model fit | Depends on end-stop accuracy (of the etch) or step sharpness (if a physical deposition mask is used) |
Index range | not any limits | not any limits | not any limit | No index measurement | No index measurement |
Index accuracy | not known | not known | not know | not relevant | not relevant |
Wavelength range | 400-1000 nm (with UV source down to 250nm) | 210-1690 nm | 350-950 nm | Cu Kα radiation (1.5406 Å) | Not relevant |
What kind of thin films can be measured | Any film that is transparent to the light in the given wavelength range
ex:
|
Any film that is transparent to the light in the given wavelength range
ex:
|
In principle any film that is transparent to the light in the given wavelength range. It is limited by the refractive index files in the software and only one model (Cauchy)
ex:
|
Any film that is transparent to the X-rays
including thin layers of metals directly on Si wafers |
|
Substrate size |
|
|
|
|
Limited by the etching method and the stylus profiling instrument. |
Allowed materials |
|
|
|
|
|
Comments |
If no model exists for your layer structure, developing a model may require some work. The instrument has many models available already. |
Measurement and analysis quite time consuming. Can determine layer roughness and density including density gradients |
Direct measurement. |