B. Rong

Inductively coupled plasma etching of GaN and its effect on electrical characteristics

Dry etch behavior in the inductively coupled plasma processing of GaN using SF6/N2 plasma has been found to be highly ion induced with an ion energy threshold of about 100 eV. Temperature dependence of the etch rate indicates a small kinetic component. Maximum etch rate of 67 nm/min and good anisotropy have been demonstrated. The most efficient etch regime is observed for an ICP source power between 500–1000 W where the etch mechanism is ion limited. In contrast to reactive ion etching induced damage behavior, almost ideal diodes are obtained at the higher dc bias condition (300 V). X-ray photoelectron spectroscopy and atomic force microscopy studies indicate that smooth surface with minimal surface contamination, coupled with the incorporation of N on the substrate surface help to produce ideal diodes on surfaces etched at 300 V. Sidewall depletion is found to be in the range of 65 nm at the given SF6/N2 plasma process conditions.

High resolution reactive ion etching of GaN and etch-induced effects

We have developed a process using electron beam lithography and reactive ion etching for the high resolution pattern transfer of GaN. 150 nm dots have been fabricated in GaN successfully. Photoluminescence, scanning electron microscopy, and x-ray photoelectron spectroscopy have been employed to compare the damage inflicted on the GaN surfaces after SF6 and Ar plasma exposures. Near-band-edge luminescence analysis indicates the existence of a higher concentration of donors on the top 100 nm of the GaN surface after Ar as supposed to SF6 plasma exposure. An order of magnitude decrease in the ratio of the yellow to the band-edge luminescence intensity is found in the samples subjected to lower ion energies. Formation of pits is observed on the substrate surfaces after plasma treatment. Nitrogen deficient surfaces limited to the top few monolayers, as well as defect propagation down to 100 nm, exist in our plasma exposed GaN samples.

X-ray photoelectron spectroscopy studies of the effects of plasma etching on amorphous carbon nitride films

The effects of post-treated oxygen plasma etching procedures have been investigated for amorphous carbon nitride (a-C:N) films deposited by dc magnetron sputtering. X-ray photoelectron spectroscopy (XPS) has been used to study the microstructure of these films. It has been found that the relative concentration of the beta-C3N4-like phase in the a-C:N films is enhanced significantly by oxygen plasma etching and by increasing the dc bias voltages during the etch experiments. This study reveals that an oxygen plasma can work as an effective chemical etchant for the graphite-like carbon-nitrogen phase in a-C:N films. This suggests a very promising way of obtaining harder a-C:N films.

Effects of reactive ion etching on the electrical characteristics of GaN

We present an investigation of the electrical characteristics of plasma exposed GaN. The specific contact resistance of ohmic contacts fabricated on GaN after argon plasma bombardment for 2.5 min at 0.03 W/cm2 are measured to decrease by a factor of 4 compared to the unetched surface. Gold has been found to be the best material for GaN Schottky diode. A study of the electrical performance of diodes fabricated on plasma exposed GaN has been undertaken. To compare the effect of the chemical versus physical factors, as well as the role played by the ion mass of the etchant species during the etching process on diode behavior, GaN surfaces have been exposed to Ar, N2, as well as SF6+N2 plasmas before diode fabrication. Our data indicate that a plasma with low ion mass etchant species or a dominant chemical mechanism of etching with a high etch rate creates less surface damage. The use of a SF6+N2 plasma should be possible for GaN transistor gate recessing.

Fabrication of two dimensional GaN nanophotonic crystals (31)

The authors have investigated chlorine based inductively coupled plasma etching of GaN by using different gas mixtures of Ar, Cl2, and N2. The etch mechanism and N2 role have been studied. We found that both ion energy and ion current density are important. The N2 plays a multiple role in etching GaN, chemical reaction, and ion bombardment. A reliable process to fabricate GaN nanophotonic crystals has been developed. Plasma conditions have been optimized toward a balance of ion current density, ion energy, and chemical species density. As a result, flat bottom, anisotropic photonic crystal with a=215nm d=129nm has been fabricated at an etch rate of 320nm∕min and an etch depth of 650nm. For comparison, an etch rate of 530nm∕min has been obtained in etching trench lines down to 1.61μm deep with a width of 500nm. The developed process has been used to fabricate GaN photonic crystal (PC) waveguides for 1.55μm wavelength. Transmission measurements reveal the ΓM stop band in hole type PC and illustrate the feas...

A study of reactive ion etching damage effects in GaN

Abstract This paper presents a study of dry-etch-induced damage effects on GaN films grown on SiC substrates. Photoluminescence (PL) of the control sample and samples exposed to Ar, SF 6 , SF 6 +N 2 and N 2 plasmas have been studied. In general, etching is found to decrease the donor-bound exciton (D°X) intensity. X-ray photoelectron spectroscopy (XPS) has been employed to analyse the surface atomic concentration of all samples. Incorporation of nitrogen has been found on GaN surfaces exposed to N-containing plasmas. Langmuir probe has been used to quantify the amount of ion bombardment during plasma etching by measuring the ion flux. The effect of etching in an N 2 plasma and annealing in an N 2 ambient on the optical properties of the GaN surface has been compared and found to be significantly different.

Etch mechanism and etch-induced effects in the inductively coupled plasma etching of GaN

The inductively coupled plasma (ICP) processing of gallium nitride (GaN) using SF6/N2 and Cl2/Ar gas mixtures has been compared. ICP processing of GaN using SF6 and N2 mixture of 1:1 produces an optimized etch rate of 67 nm/min while five times higher etch rate of 314 nm/min is achieved using Cl2 and Ar mixture of 1:3. Etch mechanism studies indicate an ion-induced, coupled with a large chemical enhancement component for both SF6/N2 and Cl2/Ar inductively coupled plasma etching. From electrical diode characterization, an increase in electrical degradation with increasing dc bias in Cl2/Ar plasma is observed, while an improvement of diode characteristics is evident after etching in SF6/N2 plasma. X-ray photoelectron spectroscopy results indicate the presence of a significantly Ga deficient surface after etching GaN in Cl2 and Cl2/Ar plasmas. Correlation between etch mechanism and etch-induced damage results strongly indicates the existence of ion-induced chemical damage in the ICP etching of GaN in Cl2 and...

Transmission measurement of the photonic band gap of GaN photonic crystal slabs

A high-contrast-ratio (30 dB) photonic band gap in the near-infrared transmission of hole-type GaN two-dimensional photonic crystals (PhCs) is reported. These crystals are deeply etched in a 650 nm thick GaN layer grown on sapphire. A comparison of the measured spectrum with finite difference time domain simulations gives quantitative agreement for the dielectric band and qualitative agreement for the air band. The particular behavior of the air band arises from the relatively low index contrast between the GaN layer and the sapphire substrate. Our results call for extension of the operation of GaN PhCs to the visible range.

2D InP photonic crystal fabrication process development

We have developed a reliable process to fabricate high quality 2D air-hole and dielectric column InP photonic crystals with a high aspect ratio on a STS production tool using ICP N2+Cl2 plasma. The photonic crystals have a triangular lattice with lattice constant of 400 nm and air-hole and dielectric column radius of 120 nm. Large efforts have been devoted on developing a proper mask. We obtained a perfect, clean and vertical profiled SiNX mask. The next main effort is InP pattern transfer in Cl2+N2 plasma. Etching selectivity, smooth sidewall and etch profile are directly related to plasma process condition, besides the quality of SiNX mask. We have optimized the N2+Cl2 plasma condition to obtain high aspect ratio, vertical profile and smooth sidewall InP structures. Cylindrical holes (2 micron depth) and rodlike pillars (2.4 micron height) are uniformly fabricated. An aspect ratio of 18 for 100nm trench lines has been obtained. AFM measurement evidences that etched surfaces are smooth. The root mean square roughness of pillar and hole is 0.7 nm and 0.8 nm, respectively. The optical transmission characterization of ridge waveguides has been carried out. Transmission spectrum of 1 micron wide waveguide has been obtained.