1. Testing the adhesion of thin film to substrate
Student Talk
Tia Lohtander

2. Buckling delamination of DLC film on Si substrate.
Image from:

3. Adhesion Durability and performance of thin film device
Sum of several factors
There is no one specific quantitative parameter
Contradictory results from different tests
Possible types of interfaces
Image from: Franssila S. Introduction to Microfabrication. John Wiley & Sons Chapter 7. ISBN:

4. Selection of test method
Simple tests
Industrial use
Estimation of thin film quality
Simple set-up
Complex tests
Research use
More precise quantitative results
Sample preparations and expensive equipment
For example: Pulsed laser or cross-section indentation

5. Scratch test set-up
Image from:

6. Results Critical load = “adhesion value”
Frictional force, depth and visual changes
Image from: Lee J-E. et al.Assessment of adhesion between thin film and silicon based on a scratch test. Journal of Material Science and Technology doi: /s

7. Limitations and problems
Most useful for hard coatings deposited on softer substrates
Standards only for some cases
Lack of data
Safest compare data to results from same test method
SEM image from scratch test of 100 nm Al film on stainless steel.
Image from: Bull S.J. & Berasetegui E.G. An overview of the potential of quantitative coating adhesion measurement by scratch testing. Tribology International doi: /j.triboint

8. References
[1] Bull S.J. & Berasetegui E.G. An overview of the potential of quantitative coating adhesion measurement by scratch testing. Tribology International doi: /j.triboint [2] Franssila S. Introduction to Microfabrication. John Wiley & Sons Chapter 7. ISBN: [3] Lee J-E. et al. Assessment of adhesion between thin film and silicon based on a scratch test. Journal of Material Science and Technology doi: /s [4] technology/testing-equipment/scratch-tester/

9. Detailed information: Why to test?
2 main failure modes for thin films: buckling and wedge spallation
Adhesion is sum of many things. For example it depends on pre treatments like cleaning the substrate, deposition technique, substrate roughness, will the atoms are chemisorped or physisorped to substrate and if adhesive film is used or not etc.
 Interface structure (see slide 3) also impacts on adhesion
We want to prevent debonding and delamination because it impacts directly to the lifetime and performance of thin film device

10. Detailed information: How to test?
Basic adhesion= chem. bonds across the interface
Practical adhesion= Film adhesion is often characterized by the strain energy released per unit in delamination area, practical adhesion basically gives method-specific measurement.
Various ways to test: simple ones (peel tape test, pull- off, scratch) and more difficult ones (cavitation, laser acoustics)
selection depending on how accurate results needed

11. Detailed information: Scratch test (1)
Rockwell diamond tip moves across the film at a constant velocity. At the same time applied normal force is steadily increased. The diamond tip causes stress between the thin film/substrate interface causing delamination of film.
The load that breaks the film is called critical load and can be used to describe adhesion in scratch tests.
Depends on set-up parameters and materials of film and substrate
The beginning of delamination and the critical load can be detected by observing changes in friction, viewing the sample with optical microscope and measuring the depths of scratches by AFM
The hardness of substrate and film affects how big critical load is needed.
The scratch test most suitable for hard coatings

12. Detailed information: Scratch test (2)
The test set-up is quite simple but comparing the results is not reliable always, especially between different tests
Standards for some cases: e.g. ASTM C for hard thin ceramic coatings on metal or ceramic substrates
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