Application Note | Thin Film Inspection
Optoelectronic Film Surface Inspection Using 3D Profilometry
Defect Sizing, Zone Roughness and Pass/Fail Roughness Maps on a Coated Silicon Wafer
Research & Experimental Testing
Duanjie Li & Andrea Novitsky
Visual Design & Editorial
Andrew Shore
Introduction
Optoelectronic devices and systems convert visible or infrared radiation to electrical signals. Thin-film optoelectronic devices have a wide variety of applications, including photocells, solar cells and LEDs, etc. The continual development of the optoelectronic thin films and the associated technologies such as impurity incorporation, etching and surface chemistry aims for improving the photoconversion at micro or nano scale levels.
Importance of 3D Profilometry for Optoelectronic Films
Surface roughness and texture of the optoelectronic film is critical in the final product quality. Good surface quality can increase the optical efficiency and reduce the heat resistance. High-efficiency thin-film solar cells require defect-free surface finish to achieve the best conversion efficiency. A reliable and quantitative measurement of the surface texture and consistency of the optoelectronic film allows proper optimization of the deposition technique during the R&D stage and rigorous inspection in quality control. The NANOVEA 3D Non-Contact Profilometers utilize chromatic confocal technology with unique capability to precisely measure the sample surface.
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Measurement Objective
In this study, the NANOVEA PS50 non-contact profilometer is used to measure the surface texture of different areas of an optoelectronic film coated on a silicon wafer. We showcase the capacity of the NANOVEA non-contact profilometer in providing precise 3D profile measurement and in-depth analysis of the optoelectronic film.
NANOVEA PS50 Compact
Optical Profilometer
Results and Discussion
An optoelectronic film with two areas of different surface textures is evaluated in this study. In the following report, we will analyze these two areas in detail.
Detailed Results: Area A
The false color view and 3D view of Area A are shown in Figure 2 and Figure 3, respectively. The roughness values of Area A calculated based on the ISO 25178 standard are also summarized in Figure 2. The surface of the film is fairly smooth in general. However, a small bump is present at the center of the scan area, which results in a higher roughness value Sq of ~1 µm.
| ISO 25178 parameter, Area A | Value |
|---|---|
| Sa | 0.2006 µm |
| Sq | 1.066 µm |
| Sp | 24.16 µm |
| Sv | 0.9205 µm |
| Sz | 25.08 µm |
| Ssk | 16.84 |
| Sku | 319.6 |
| Sdar | 1012648 µm² |
| Spar | 1000000 µm² |
Table 1: Roughness of Area A (from Fig. 2).
The size and volume of the central bump is further analyzed as shown in Figure 4. The bump has a surface area of 12570 µm², a maximum height of 24 µm and a volume of 76481 µm³, respectively. Such information of the peculiar surface feature enables users to precisely assess the size and shape of the surface defect and imperfections, so as to further optimize the film deposition process to stimulate the growth of desired surface texture while restraining the formation of the unwanted ones.
Detailed Results: Area B
The false color view and 3D view of Area B are shown in Figure 5 and Figure 6, respectively. Area B does not possess the prominent bump present in the surface center of Area A. Area B exhibits two zones with different texture and roughness. Zone 1 possesses a coarser surface texture with an average Sq roughness value of 0.214 µm, compared to the Sq of 0.0624 µm for Zone 2. The average Sq roughness value of Area B is 0.128 µm.
| ISO 25178 parameter | Area B | Zone 1 | Zone 2 |
|---|---|---|---|
| Sa (µm) | 0.072 | 0.157 | 0.0402 |
| Sq (µm) | 0.128 | 0.214 | 0.0624 |
| Sp (µm) | 1.88 | 1.52 | 1.33 |
| Sv (µm) | 0.806 | 0.829 | 0.205 |
| Sz (µm) | 2.69 | 2.34 | 1.54 |
| Ssk | 3.38 | 0.932 | 5.00 |
| Sku | 26.3 | 5.63 | 70.0 |
Table 2: Roughness of Area B and its two zones (from Fig. 5).
Figure 7 shows the 2D profile analysis of Area B as an example. The two zones with different roughness and texture exhibit clearly different surface height variations. The asperities in the rougher zone have a height up to ~0.6 µm.
The Rq Roughness Distribution Map of Area B as shown in Figure 8a provides an ideal tool to study the local surface properties of the scanned sample, allowing users to easily assess the roughness values of the surface features of interest. Figure 8b shows an example of the Pass/Fail Maps generated by the Analysis Software based on different Roughness Thresholds. The rough areas are highlighted in red when their surface roughness is above a certain set threshold value. This provides a tool for the user to determine the quality of the sample surface based on a target roughness threshold.
Conclusion
In this application, we have showcased that the NANOVEA 3D Non-Contact Profilometer provides a comprehensive in-depth study of the surface texture on an optoelectronic film. The surface finish plays a critical role in the service quality of the optoelectronic films. The high resolution scan and comprehensive analysis tools including 3D and roughness mapping analyses by the NANOVEA profilometer enable quantitative evaluation of the surface finish, which is critical in evaluating and optimizing the product quality of the optoelectronic film.
The data shown here represents only a portion of the calculations available in the analysis software. NANOVEA Profilometers measure virtually any surface in fields including Semiconductor, Microelectronics, Solar, Fiber Optics, Automotive, Aerospace, Metallurgy, Machining, Coatings, Pharmaceutical, Biomedical, Environmental and many others.
Frequently Asked Questions About Optoelectronic Film Inspection
Why does surface finish matter for optoelectronic films?
Good surface quality can increase optical efficiency and reduce heat resistance, and high-efficiency thin-film solar cells need a defect-free finish for the best conversion efficiency.
Can a profilometer size a surface defect?
Yes. A bump in the center of Area A was measured at a surface area of 12570 µm², a maximum height of 24.24 µm and a volume of 76481 µm³, so its size and shape can be assessed precisely.
How rough were the film areas?
Area A had an Sq of 1.066 µm, raised by the bump. Area B averaged 0.128 µm, with a coarser zone at 0.214 µm and a smoother zone at 0.0624 µm.
What is a pass/fail roughness map?
The software computes local roughness over small windows (here 15 × 15 points) and highlights in red the areas above a set threshold; in Area B, 13.1 % of the projected area exceeded a 157 nm threshold.
How is this used in production?
Reliable, quantitative texture measurement supports optimizing the deposition technique during R&D and rigorous inspection in quality control.
Which instrument was used?
The NANOVEA PS50 3D non-contact profilometer, using chromatic confocal technology.
