A bow-free freestanding GaN wafer

Area of Science:

• Materials Science
• Semiconductor Manufacturing

Background:

• Freestanding gallium nitride (GaN) wafers are crucial for high-brightness light-emitting-diodes (LEDs).
• Achieving bow-free GaN wafers is challenging due to inherent stress and fabrication complexities.

Purpose of the Study:

• To develop a process for fabricating 2-inch diameter, bow-free freestanding GaN wafers.
• To optimize GaN wafer fabrication for high-brightness LED applications.

Main Methods:

• Utilized hydride-vapor-phase epitaxy (HVPE) to grow pit and mirror GaN layers.
• Employed laser lift-off (LLO) and multi-step polishing (diamond abrasives: 3.0 μm, 0.5 μm, 50 nm) for wafer shaping.
• Incorporated N-face polishing and inductively-coupled-plasma reactive-ion etching (ICP-RIE).

Main Results:

• Successfully fabricated a ∼185 μm thick, 2-inch freestanding GaN wafer with reduced curvature.
• Demonstrated that controlling Ga-face mirror layer removal during polishing significantly impacts wafer bow.
• Observed a strong correlation between wafer bow and residual stress after polishing.

Conclusions:

• The developed process effectively minimizes wafer bow in freestanding GaN.
• The process enables the production of high-quality GaN wafers suitable for advanced LED applications.
• Controlling residual stress is key to achieving near-bow-free GaN wafers.