Reactive ion etching of gallium nitride in silicon tetrachloride plasmasa)

As III-V nitride devices advance in technological importance, a fundamental understanding of device processing techniques becomes essential. Recent works have exposed various aspects of etch processes. The most recent advances and the greatest remaining challenges in the etching of GaN, AlN, and InN are reviewed. A more detailed presentation is given with respect to GaN high density plasma etching. In particular, the results of parametric and fundamental studies of GaN etching in a high density plasma are described. The effect of ion energy and mass on surface electronic properties is reported. Experimental results identify preferential sputtering as the leading cause of observed surface non-stoichiometry. This mechanism provides excellent surfaces for ohmic contacts to n-type GaN, but presents a major obstacle for Schottky contacts or ohmic contacts to p-type GaN. Chlorine-based discharges minimize this stoichiometry problem by improving the rate of gallium removal from the surface. In an effort to better understand the high density plasma etching process for GaN, in-situ mass spectrometry is employed to study the chlorine-based high density plasma etching process. Gallium chloride mass peaks were monitored in a highly surface sensitive geometry as a function of microwave power (ion flux), total pressure (neutral flux), and ion energy. Microwave power and pressure dependencies clearly demonstrate the importance of reactive ions in the etching of wide band gap materials. The ion energy dependence demonstrates the importance of adequate ion energy to promote a reasonable etch rate (≥ 100-150 eV). The benefits of ion-assisted chemical etching are diminished for ion energies in excess of 350 V, placing an upper limit to the useful ion energy range for etching GaN. The impact of these results on device processing will be discussed and future needs identified.

Section: Reactive Ion Etchingmentioning

confidence: 69%

Etch Processing of III-V Nitrides

Eddy

1999

“…The etch rates reported for GaN using RIE with various etch chemistries range from 17 to 100 nm/min [11][12][13][14][15]. Etch rates were found to depend strongly on the plasma self-bias voltage, and essentially independent of the chamber pressure for pressures less than 80 mTorr [13].…”

Section: Etch Rates and Profilesmentioning

confidence: 99%

“…They include ion milling [6,7], chemically assisted ion beam etching (CAIBE) [8,9,55], reactive ion beam etching (RIBE) [10], reactive ion etching (RIE) [11][12][13][14][15], electron-cyclotronresonance reactive ion etching (ECR-RIE) [16][17][18][19][20][21], and inductively-coupled-plasma reactive ion etching (ICP-RIE) [22][23][24][25][26][27]. Optical excitation sources with photon energies higher than the bandgap energies of the semiconductors have been applied to both dry and wet etching methods.…”

Section: Dry Etchingmentioning

confidence: 99%

Dry and Wet Etching for Group III – Nitrides

Adesida

Youtsey

Ping

et al. 1999

Self Cite

The group-III nitrides have become versatile semiconductors for short wavelength emitters, high temperature microwave transistors, photodetectors, and field emission tips. The processing of these materials is significant due to the unusually high bond energies that they possess. The dry and wet etching methods developed for these materials over the last few years are reviewed. High etch rates and highly anisotropic profiles obtained by inductively-coupled-plasma reactive ion etching are presented. Photoenhanced wet etching provides an alternative path to obtaining high etch rates without ion-induced damage. This method is shown to be suitable for device fabrication as well as for the estimation of dislocation densities in n-GaN. This has the potential of developing into a method for rapid evaluation of materials.

“…Addition of fluorine in the form of SiF 4 has been investigated in an attempt to form a volatile group-V fluoride e.g. NF x , but additions of SiF 4 to a SiCl 4 based plasma did not increase the GaN etch rate [6]. Possibly, this reaction mechanism is thermodynamically "uphill» or the formation of involatile GaF x impedes the chemical reaction.…”

Section: Introductionmentioning

confidence: 99%

ECR RIE-Enhanced Low Pressure Plasma Etching of GaN/InGaN/AlGaN Heterostructures

Humphreys

Govett

1996

A room temperature (RT) plasma etch process has been developed to non-selectively etch GaN/InGaN/AlGaN structures, grown on sapphire substrates, using an electron cyclotron resonance (ECR) plasma source with RIE enhancement. The process chemistry chosen was Cl 2 /CH 4 based in order to facilitate the formation of volatile etch by-products, typically to form group III halides and group V hydrides, although indium is more likely to form an organo-metallic compound as opposed to a chloride. A characteristic of this process is the very smooth sidewall features obtained and the controllability of the etch profile via ECR power, table bias and/or gas flow ratio. Typical results obtained using a RT process were etch rate above 100 nm/min., selectivity to resist mask above 30:1 and smooth anisotropic profile at low ion-energies (below 100 eV). The process etch rate showed a characteristic increase with increasing table bias (above 130 nm/min.) with only small changes in the relative etch rate of each compound (i.e. selectivity maintained at roughly 1:1), however, this etch does rely upon competing etching and deposition mechanisms and thus too large a variation in one parameter without a corresponding compensation with another leads to a rough surface and a more selective etch. The process has also been demonstrated using a metal mask (e.g. Ni) and present work is progressing onto other gas combinations and the use of high temperature electrodes.