Using 3D Profilometry for Optoelectronic Film Surface Inspection

Table of Contents

Introduction
Importance of 3D Profilometry for Optoelectronic Films
Measurement Objective
Results and Discussion
Detailed Results - Area A:
Detailed Results - Area B:
Conclusion

Introduction

Visible or infrared radiation is converted to electrical signals by optoelectronic devices and systems. Thin-film optoelectronic devices have a wide range of applications, such as LEDs, solar cells, photocells, etc. The constant development of the optoelectronic thin films and the related technologies such as surface chemistry, etching, and impurity incorporation aims for enhancing the photoconversion at micro or nano scale levels.

Importance of 3D Profilometry for Optoelectronic Films

Surface roughness and texture of the optoelectronic film greatly influences the quality of the final product. Good surface quality can reduce the heat resistance and increase the optical efficiency. High-efficiency thin-film solar cells need defect-free surface finish in order to attain the best conversion efficiency. A dependable and quantitative measurement of the surface texture and consistency of the optoelectronic film enables proper optimization of the deposition technique during the R&D stage and stringent inspection in quality control. The Nanovea 3D Non-Contact Profilometers utilizes chromatic confocal technology with exclusive capability to precisely measure the surface of the sample.

Measurement Objective

In this analysis, 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. Also demonstrated is the capacity of Nanovea non-contact profilometer in providing precise 3D profile measurement and detailed analysis of the optoelectronic film.

Optical sensor scanning

Figure 1. Optical sensor scanning on the surface of the optoelectronic film sample.

Results and Discussion

In this study, an optoelectronic film with two areas of different surface textures is evaluated. In the following section, these two areas are analyzed in detail.

Detailed Results - Area A:

The false color view and 3D view of Area A can be seen in Figures 2 and 3, respectively. The roughness values of Area A computed based on the ISO 25178 standard is also summed up in Figure 2. Generally, the surface of the film is relatively smooth, but the presence of a small bump at the middle of the scan area leads to a higher roughness value Rq of ~1 µm.

False color view and roughness parameters

Figure 2. False color view and roughness parameters for Area A.

3D view for Area A

Figure 3. 3D view for Area A.

Further analysis of the size and volume of the central bump is carried out as shown in Figure 4. The bump has a maximum height of 24 µm, a volume of 76481 µm3, and a surface area of 12570 µm2. Such information of the peculiar surface feature allows users to precisely assess the shape and size of the surface defect and imperfections, in order to further optimize the film deposition process to stimulate the growth of desired surface texture and restrain the formation of the unwanted ones.

Size and volume of the bump in Area A

Parameters Unit Peak
Surface µm2 12570
Volume µm3 76481
Max. depth/height µm 24.24
Mean depth/height µm 6.084

Figure 4. Size and volume of the bump in Area A.

Detailed Results - Area B:

Figures 5 and 6 show the false color view and 3D view of Area B, respectively. Area B does not possess a prominent bump present in the surface center of Area A, while Area B displays two zones with different roughness and texture. Zone 1 has a coarser surface texture with an average Rq roughness value of 0.214 µm, as opposed to the Zone 2 Rq of 0.0624 µm. 0.128 µm is the average Rq roughness value of Area B.

False color view and roughness parameters

(b) Area B: (c) Zone 1: (d) Zone 2:
ISO 25178 ISO 25178 ISO 25178
Height Parameters Height Parameters Height Parameters
Sq 0.128 µm Sq 0.214 µm Sq 0.0624 µm
Ssk 3.38 Ssk 0.932 Ssk 5.00
Sku 26.3 Sku 5.63 Sku 70.0
Sp 1.88 µm Sp 1.52 µm Sp 1.33 µm
Sv 0.806 µm Sv 0.829 µm Sv 0.205 µm
Sz 2.69 µm Sz 2.34 µm Sz 1.54 µm
Sa 0.072 µm Sa 0.157 µm Sa 0.0402 µm

Figure 5. False color view and roughness parameters for Area B.

3D view of Area B.

Figure 6. 3D view of Area B.

The 2D profile analysis of Area B is shown as an example in Figure 7. The two zones with different texture and roughness show clearly different surface height variations. The asperities in the rougher zones have a height up to ~0.6 µm.

Profile extraction and amplitude parameters for Area B.

ISO 4287
Amplitude parameters - Primary profile
Pa 0.07919 µm
Pt 1.039 µm

Figure 7. Profile extraction and amplitude parameters for Area B.

Figure 8a shows the Rq roughness Distribution map of Area B that serves as an ideal tool for studying the local surface properties of the scanned sample, enabling users to easily assess the roughness values of the surface features of interest. Shown in Figure 8b is an example of Pass/Fail Maps generated by the analysis software based on different roughness thresholds. The rough areas are emphasized in red when their surface roughness exceeds a certain set threshold value. This gives a tool for the user to establish the sample surface quality based on a target roughness threshold.

Map local properties study

Figure 8. Map local properties study, Rq with window size 15x15points for Area B.

Conclusion

In this application, it was demonstrated that the Nanovea 3D Non-contact Profilometer provides comprehensive, in-depth study of the surface texture on an optoelectronic film. The surface finish plays a crucial role in the service quality of optoelectronic films. The high-resolution scan and comprehensive analysis tools including 3D and roughness mapping analyzes by Nanovea profilometer allow quantitative evaluation of the surface finish, which is essential in optimizing and evaluating the product quality of the optoelectronic film.

The data cited here represents only a portion of the calculations available in the analysis software. Nanovea Profilometers measure almost any surface in fields including microelectronics, semiconductor, fiber optics, solar, aerospace, automotive, machining, metallurgy, coatings, biomedical, pharmaceutical, environmental, and others.

Nanovea

This information has been sourced, reviewed and adapted from materials provided by Nanovea.

For more information on this source, please visit Nanovea.

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