Laser etching of GaN

Laser etching of GaN

Jonathan Winterstein

Dr. Tim Sands, Advisor

Outline

•Introduction

•Experimental process

•Results

•Conclusions

Introduction

•Gallium Nitride is a wide-band-gap semiconductor (Eg = 3.4 eV) with potential applications as:

• Blue LEDs or Laser diodes.

•And researchers have also suggested GaN could be used for transistors.

•GaN resists chemical etching, laser etching is a possible alternative.

•Laser etching should be less expensive and less damaging to specimens than current industry etching methods such as Reactive Ion Etching

Introduction: Technical aspects

•Laser etching of GaN works by raising the temperature of the GaN above a decomposition temperature of around 900° C.

•The GaN heated above this temperature decomposes into gallium metal and nitrogen gas. The gallium metal solidifies and remains on the sample surface.



•The GaN heated above this temperature decomposes into gallium metal and nitrogen gas. The gallium metal solidifies and remains on the GaN surface.



•The GaN heated above this temperature decomposes into gallium metal and nitrogen gas. The gallium metal solidifies and remains on the sample surface.

•The gallium is reflective and could reduce the etch rate because some laser energy would not reach the GaN surface.

•For this study all samples are processed using a KrF excimer laser producing 248 nm wavelength light for a 25 nanosecond pulse.

Outline

•Introduction


•Results

•Conclusions

Experimental Process

Experiment 1: Ga removal in HCl bath as a function of time and temperature.

•GaN samples on sapphire substrates are irradiated once with the laser at a fluence of 800 mJ/cm2

•Residual Ga is cleaned in HCl baths for times of 30 seconds and 5 minutes at room temperature (26-27° C), 40° C, 50° C and 60° C.

•Optical microscopy is used to compare amount of Ga removed for each sample.


Experiment 2: Laser etch rate as a function of time in HCl bath.

•Samples receive 10 laser pulses at a fluence of 700 mJ/cm2 and are cleaned in HCl for times of 30, 60, 120, 150 and 300 s at 50° C between each laser pulse.

•Amount of GaN removed determined by profilometry.


Experiment 3: Etch rate as a function of laser fluence.

•Samples receive 10 or 15 laser pulses at fluences ranging from 550 to 825 mJ/cm2.

•Between laser pulses, Ga is removed by cleaning in HCl bath at 50° C for 3 minutes.

•Amount of GaN removed is determined by profilometry.

Outline

•Introduction


•Results

•Conclusions

Results

Temperature: 50° C

30 seconds 5 minutes

Results

Results for Experiment 2.

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Results

Results for Experiment 3.

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Yang et al Winterstein

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Yang et al Winterstein Senior Research Group

Outline

•Introduction


•Results

•Conclusions

Conclusions

•Etching effectively stops near 550 mJ/cm²

•A significant drop in etching rate occurs as the fluence decreases from 700 to 600 mJ/cm².

•A saturation point appears to occur near 750-800 mJ/cm². Saturation occurring at this fluence follows the trend of the results published by Yang et al.

•Thirty seconds in HCl bath is not sufficient to remove residual gallium.

•Etching without cleaning between pulses significantly reduces etch rate.

•Future work might include studying laser etching under vacuum conditions and GaN film transfer through laser liftoff.

Thank You.

Any Questions?

http://ece-www.colorado.edu/~bart/book/gaussian.xls

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Laser etching of GaN