Gold Etchant Characterization

• Virtual reality has emerged as a promising technology for next generation digital displays. 
• An important component of virtual reality are micro LEDs  (µLED), which are used in digital displays. 
• Patterning wafers with microstructures is crucial for µLED manufacturing, but presents an industry challenge because of their small size. Gold etching using wet etch techniques is a favorable approach to manufacturing microstructures.
• The patterns are composed of a sputtered gold layer by chemical vapor deposition and an electroplated gold layer by electrochemical deposition.
• Wet etching uses a reactive solution to evenly remove material from a surface. 
• This is a popular method because it has low energy and equipment costs.

Process conditions must:

• Not exceed received concentration of etchant.
• Remain below 50℃.
• Not exceed 20 minutes.
• Recirculate the etchant.
• Etch rate needs to be less than 2 nm/s (limitation of test system in Ireland).

Project must:

• Analyze effect of temperature, time, flow rate, and concentration on the etch rate of sputtered and electroplated gold.

• Characterize an etching process that etches 90 nm of sputtered gold and no more than 150 nm of electroplated gold.

The etch cell design allows etchant to be pumped through the bottom of the cell and overflow out of a channel in the lid. The etch cell and flow system were designed to be scalable to the recirculation system used at Meta’s wafer fabrication lab.

We ran trials varying time, concentration, flow rate and temperature.

Kapton tape is placed on the wafer sample is submerged in the etchant and the trial is run, then the sample is cleaned and the tape is removed. The Kapton tape is impermeable to the etchant so it allows the section under it to remain unetched while the rest of the sample is being etched. This produces a step that can be measured from the unetched to the etched portion in order to find the etch rate. These measurements are taken on an optical interferometer.