Automated Optical Metrology of Solar Cells

The performance of solar cells are based on several parameters that include film thickness, substrate texture, accurate contact finger formation and wafer edge quality. The Zeta-200 Automated 3D Measurement System offers true color imaging and analysis of complicated surfaces in lower than one minute for each site. Using the innovative and in-house developed ZDot technology, it is possible to measure almost all types of surfaces from include highly smooth to highly rough.

Solar Cell Process Characterization

Texture Surface Area Ratio on Mono and Poly Silicon

Pyramid structures are etched on the wafer surface to improve solar cell light absorption, as shown in the Zeta 3D image below. A standard Zeta recipe counts and analyzes pyramids in the field of view, then a sequence repeats the analysis on different sites across the wafer.

Film Thickness Measurement

A white light spectrometer determines film thickness from 30 nm to 10 µm thick, even on rough, textured silicon surfaces.

Convenient Edge Inspection Module

Etching or polishing processes are used to remove conductive areas from the wafer edge, but can cause damage. A Zeta 3D image of a wafer edge is shown below. Several cross sections of the wafer edge showing shape and roughness are shown at right.

Automated Contact Finger Detection and Inspection

The Zeta-200 system enables the automation of the analysis of metal contact fingers using high dynamic range imaging. The features of high dynamic range imaging are listed below:

• Auto-focus enables detection of the wafer surface.
• Pattern recognition enables to determine the metal pattern and arrange the same at the image center.
• Recipe-defined scan parameters control the vertical range and adjust the illumination to accommodate extremely low reflectivity (nitride-coated) and high reflectivity (metal) surfaces.
• Analysis software automatically determines the height and width of various cross sections.
• Optional sequences repeat the measurement on sites across the wafer.

Zeta Solar Package

Zeta 3D Software examines standard 2D or 3D wafer images for general surface characterization that include the following:

• Step height
• Surface roughness
• Feature size, diameter, area, and volume
• Wafer bow
• Film Thickness
• 3D surface visualization in true color
• Statistics

Several configurations of the system are available that include the following:

• Zeta-20 manual load system for R&D
• Zeta-200 system with automated XY stage
• Optional edge measurement fixture
• Optional Film Thickness measurement
• Vacuum chucks for wafers of different sizes
• Piezo stage for 2nm height resolution

Customized solar cell analysis software includes production-ready recipes to enable substrate texture characterization and contact finger inspection.

About Zeta Instruments

Zeta Instruments is a leading provider of precision microstructure and surface measurement systems that enable manufacturers of green-technology and bio-medical products to substantially improve yields and quality control. Zeta’s advanced metrology solutions provide direct benefit to the production of high-brightness LEDs, solar cells, micro-fluidics/bio-technology and magnetic storage media. Our patented Z-Dot™ technology enables manufacturers to quickly and accurately perform 3D measurement of the micron-scale features of these applications, positioning it as a strategic supplier to these high-growth industries.

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

For more information on this source, please visit Zeta Instruments.