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Material Deposition and Device Fabrication in the Copper Indium Gallium Diselenide Cluster Tool

This page provides additional details on material deposition and device fabrication in the Copper Indium Gallium Diselenide (CIGS) cluster tool.

Techniques involve deposition of CIGS layers and non-CIGS layers.

CIGS Deposition

Photo of man in white lab coat examining part of the UHV evaporator/CIGS deposition tool, which is attached to the CIGS cluster tool.  The metal cylindrical chamber has various protruding flanges, and flexible hoses descend from the ceiling of the lab to bring liquid nitrogen to the deposition chamber.

Ultra-high-vaccum evaporator/CIGS deposition tool, which is attached to the Copper Indium Gallium Diselenide cluster tool.

Physical vapor deposition (PVD) is the controlled condensation of a vapor on a substrate, forming a film or layer. The vapor source material is typically in the solid state and the vapor is created by a physical process—either evaporation (heating) or sputtering.

The co-evaporation chamber will deposit CIGS thin-film layers for CIGS solar cells from individual elemental sources of Cu, In, Ga, and Se. Maintained at ultra-high vacuum (UHV) pressures, this tool can analyze impurities and physical layer properties not previously possible with existing measurement and characterization tools. This chamber can deposit layers on a variety of low- and high-temperature substrates, which can then be transported in UHV to other chambers within the cluster tool, to industry tools, and to the rest of the PDIL.

The CIGS chamber has 10 source ports so that by adding specific elemental sources, the tool is capable of extensive testing of new or alternative source materials and compositions in the layer at high deposition rates. Designed to interface with industry tools, this chamber offers great flexibility and potential for industry interaction in researching specific measurement and deposition techniques for commercial use.

Applications:

  • Exploring alternative sources to costly indium, such as chalcogenides, which are compounds containing sulfides, selenides, and tellurides
  • Analyzing impurities and defects in a controlled, UHV environment
  • Investigating substrate materials
  • Investigating thickness and deposition rates of the absorber layer
  • Developing real-time diagnostics and instrumentation for thin-film quality

Special features:

  • Ultra-high vacuum at <5x10-10 torr
  • Temperatures up to 1,000°C are possible, depending on substrate
  • Deposited layers are typically between 0.5 and 2.5 µm
  • Numerous viewports
    • Ellipsometry (one is centered and the other is off-centered)
    • Residual gas analysis
    • Beam flux monitor (to measure beam intensity)
    • Optical measurement ports for transmission and reflectance spectroscopy
    • Pyrometer and variations of pyrometry
    • In-situ emission spectroscopy
    • In-situ absorption spectroscopy
    • Quartz-crystal monitors
    • Electron-impact emission spectroscopy

Non-CIGS Deposition

Various chambers can be used to deposit transparent conducting oxides (TCOs), CdS window layers, or metal contacts.

Techniques for sputtering these non-CIGS layers include radiofrequency (RF), direct-current (DC), and pulsed DC sputtering. In sputtering, a target material is exposed to a plasma made from a gas such as argon, which is not chemically reactive. The excited gas atoms hit the target and knock off atoms that deposit onto a sample surface, building up the desired film. Typically, DC sputtering is used for conductive targets such as metals, whereas RF sputtering is used for less conductive targets such as oxides.

TCO sputtering chamber

This sputtering chamber uses RF sputtering to deposit TCOs for the n and i layers—most commonly ZnO. A variety of materials can be sputtered with the three sources, and this chamber will be used to investigate ZnO and humidity-tolerant materials. We will also investigate the performance of other high-mobility materials, which, in turn, would require less initial doping. Potential research materials include indium tin oxide and magnesium zinc oxide.

CdS sputtering chamber

This chamber enables a dry process for depositing the CdS window layer in CIGS solar cells. Unlike the more common wet-chemical deposition process for CdS layers, this RF sputtering process maintains the solar cell in ultra-high vacuum for the entire fabrication time. This process also results in less waste, and thus, the potential for less expensive manufacturing of high-quality solar cells. In addition to CdS, other window materials such as ZnS and InS can be used for the three sputtering targets.

Metal contact sputtering chamber

Photo of  a rectangular metal chamber, with a circular viewing port on the left-hand edge and three other flanges to the right.  Various electrical connections and gas hoses enter various parts of the chamber. The chamber connects to the CIGS cluster tool, which is seen to the very left of the photo.

Direct-current sputtering tool for depositing back contacts on copper indium gallium diselenide devices.

This chamber will use DC sputtering for depositing metals for back contacts. The preferred metal is typically molybdenum, but other options are possible in this chamber, such as chromium, tungsten, nickel, and other refractory metals.

Special features:

  • Multi-source (three targets each)
  • Designed to be expandable for the next 10–15 years
  • Ultra-high vacuum <10-10 torr
  • Pulsed DC sputtering allows the study of fast deposition rates
  • Substrate heating up to 400°C

For more information, contact Miguel Contreras.