To study the effects of plasma chemistries on etch characteristics and plasma-induced damage to the optical properties, dry etching of ZnO films has been carried out using inductively coupled plasmas of Cl2/Ar, Cl2/H2/Ar, and CH4/H2/Ar. The CH4/H2/Ar chemistry showed a faster etch rate and a better surface morphology than the Cl2-based chemistries. Etched samples in all chemistries showed a substantial decrease in the PL intensity of band-edge luminescence mainly due to the plasma-induced damage. The CH4/H2/Ar chemistry showed the least degradation of the optical properties.

/pdf/dry-etching-of-zno-films-and-plasma-induced-damage-to-2djixydcey.pdf

Dry etching of ZnO films and plasma-induced damage to optical properties

Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.

31p-S-4 Giant Magnetoresistance in Magnetic Manganese Oxide with Intrinsic Antiferromagnetic Spin Structure

Ordered magnetic nanostructures: fabrication and properties

The field of plasma etching is reviewed. Plasma etching, a revolutionary extension of the technique of physical sputtering, was introduced to integrated circuit manufacturing as early as the mid 1960s and more widely in the early 1970s, in an effort to reduce liquid waste disposal in manufacturing and achieve selectivities that were difficult to obtain with wet chemistry. Quickly, the ability to anisotropically etch silicon, aluminum, and silicon dioxide in plasmas became the breakthrough that allowed the features in integrated circuits to continue to shrink over the next 40 years. Some of this early history is reviewed, and a discussion of the evolution in plasma reactor design is included. Some basic principles related to plasma etching such as evaporation rates and Langmuir–Hinshelwood adsorption are introduced. Etching mechanisms of selected materials, silicon, silicon dioxide, and low dielectric-constant materials are discussed in detail. A detailed treatment is presented of applications in current silicon integrated circuit fabrication. Finally, some predictions are offered for future needs and advances in plasma etching for silicon and nonsilicon-based devices.

/pdf/plasma-etching-yesterday-today-and-tomorrow-4a8eftp390.pdf

Plasma etching: Yesterday, today, and tomorrow

GaN and related materials (especially AlGaN) have recently attracted a lot of interest for applications in high power electronics capable of operation at elevated temperatures. Although the growth and processing technology for SiC, the other viable wide bandgap semiconductor material, is more mature, the AlGaInN system offers numerous advantages. These include wider bandgaps, good transport properties, the availability of heterostructures (particularly AlGaN/GaN), the experience base gained by the commercialization of GaN-based laser and light-emitting diodes and the existence of a high growth rate epitaxial method (hydride vapor phase epitaxy) for producing very thick layers or even quasi-substrates. These attributes have led to rapid progress in the realization of a broad range of GaN electronic devices, including heterostructure field effect transistors (HFETs), Schottky and p–i–n rectifiers, heterojunction bipolar transistors (HBTs), bipolar junction transistors (BJTs) and metal-oxide semiconductor field effect transistors (MOSFETs). This review focuses on the development of fabrication processes for these devices and the current state-of-the-art in device performance, for all of these structures. We also detail areas where more work is needed, such as reducing defect densities and purity of epitaxial layers, the need for substrates and improved oxides and insulators, improved p-type doping and contacts and an understanding of the basic growth mechanisms.

Fabrication and performance of GaN electronic devices

A variety of different plasma chemistries, including SF6, Cl2, ICl, and IBr, have been examined for dry etching of 6H-SiC in high ion density plasma tools (inductively coupled plasma and electron cyclotron resonance). Rates up to 4500A-min−1 were obtained for SF6 plasmas, while much lower rates (≤800A·min−1) were achieved with Cl2, ICl, and IBr. The F2-based chemistries have poor selectivity for SiC over photoresist masks (typically 0.4–0.5), but Ni masks are more robust, and allow etch depths ≥10 µm in the SiC. A micromachining process (sequential etch/deposition steps) designed for Si produces relatively low etch rates (<2,000A-min−1) for SiC.

/pdf/plasma-chemistries-for-high-density-plasma-etching-of-sic-1nopharvyu.pdf

Plasma chemistries for high density plasma etching of SiC

Critical nitride-based p-n junction issues relating to wide bandgap bipolar device performance include minority carrier lifetime, defect related current characteristics and ohmic contact properties. Recent developments in p-GaN deposition processes resulted in GaN p-i-n UV photodetectors with improved deep UV responsivity, visible light rejection and shunt resistance characteristics. From the device data, the electron diffusion length in p-GaN doped at 1·1018 cm−3 was estimated to be 790 A, and the minority carrier lifetime in the p-GaN was estimated to be 24 ps to 0.24 ns. Improved junction electrical characteristics were achieved using MBE deposition on GaN buffers grown by MOCVD. NiAu ohmic contacts were also made to p-GaN with specific contact resistances less than 10−4 Ω·cm2.

GaN PN junction issues and developments

Discrete GaN/AlGaN heterojunction bipolar transistors (HBTs) were fabricated on material grown by both metal organic chemical vapor deposition and molecular beam epitaxy. For both types of material, DC current gains of ∼10 were achieved in 90 μm emitter diameter devices measured at 300°C. Some of the key processing steps, such as ohmic contact annealing temperature and mesa fabrication by low damage dry etching, are described, together with secondary ion mass spectrometry measurements of the dopant and background impurity profiles.

GaN/AlGaN HBT fabrication

https://digital.library.unt.edu/ark:/67531/metadc668385/m2/1/high_res_d/2789.pdf

Effect of inert gas additive species on Cl2 high density plasma etching of compound semiconductors: Part I. GaAs and GaSb

Four different F{sub 2}-based gases (SF{sub 6}, NF{sub 3}, PF{sub 5}, and BF{sub 3}) were examined for high rate Inductively Coupled Plasma etching of Si. Etch rates up to {approximately}8 {micro}m/min were achieved with pure SF{sub 6} discharges at high source power (1500W) and pressure (35mTorr). A direct comparison of the four feedstock gases under the same plasma conditions showed the Si etch rate to increase in the order BF{sub 3} < NF{sub 3} < PF{sub 5} < SF{sub 6}. This is in good correlation with the average bond energies of the gases, except for NF{sub 3}, which is the least strongly bound. Optical emission spectroscopy showed that the ICP source efficiently dissociated NF{sub 3}, but the etched Si surface morphologies were significantly worse with this gas than with the other 3 gases.

/pdf/comparison-of-f-2-based-gases-for-high-rate-dry-etching-of-1mnmqhrk8i.pdf

K. B. Jung

Papers

Plasma chemistries for high density plasma etching of SiC

GaN PN junction issues and developments

GaN/AlGaN HBT fabrication

Effect of inert gas additive species on Cl2 high density plasma etching of compound semiconductors: Part I. GaAs and GaSb

Comparison of F 2 ‐Based Gases for High‐Rate Dry Etching of Si