David C. Hays

Advanced selective dry etching of GaAs/AlGaAs in high density inductively coupled plasmas

We report a breakthrough for selective etching of GaAs over AlxGa1−xAs, x=0.2, layer with a high density plasma source. This result is particularly important for III–V devices such as heterojunction bipolar transistors (HBTs) or high electron mobility transistors (HEMTs). For example, fabrication of HBTs requires a process for selective etching of a GaAs contact layer while stopping on AlGaAs layer. Inductively coupled plasma (ICP) etching with BCl3/SF6/N2/He chemistries showed extremely high selectivity of GaAs over AlGaAs (>200:1) and a photoresist (>10:1). This process also produced excellent sidewall passivation on GaAs with reasonably high rate (>1500 A /min.). Both scanning electron microscope and atomic force microscope data showed AlGaAs etch stop layer was quite smooth after processing. We found that He played a key role in enhancing selectivity and obtaining smooth AlGaAs surfaces. When used with resist masks, addition of N2 into BCl3/SF6 plasma helped formation of passivation on the sidewall an...

Ultradeep, low-damage dry etching of SiC

The Schottky barrier height (Phi(B)) and reverse breakdown voltage (V-B) of Au/n-SiC diodes were used to examine the effect of inductively coupled plasma SF6/O-2 discharges on the near-surface elec ...

Via-hole etching for SiC

Four different F2-based plasma chemistries for high-rate etching of SiC under inductively coupled plasma (ICP) conditions were examined. Much higher rates (up to 8000 A min−1) were achieved with NF3 and SF6 compared with BF3 and PF5, in good correlation with their bond energies and their dissociation efficiency in the ICP source. Three different materials (Al, Ni, and indium–tin oxide) were compared as possible masks during deep SiC etching for through-wafer via holes. Al appears to produce the best etch resistance, particularly when O2 is added to the plasma chemistry. With the correct choice of plasma chemistry and mask material, ICP etching appears to be capable of producing via holes in SiC substrates.

Dry etching of GaN and related materials: comparison of techniques

The etch rates and feature anisotropy for GaN, AlN, and InN etched in Cl/sub 2/-Ar plasmas with four different techniques were examined. Conventional reactive ion etching produces the slowest etch rates, even when high dc self-biases (>-900 V) are employed, and this leads to mask erosion and sloped feature sidewalls during ridge waveguide fabrication. Two high-ion-density techniques, inductively coupled plasma and electron cyclotron resonance, provide the highest etch rates and most anisotropic features through their combination of high-ion flux and moderate-ion energy. Etch selectivities of GaN to AlN and InN are typically /spl les/4 in these tools. Reactive ion beam etching utilizing a high density (ICP) source is also an attractive option for pattern transfer in the nitrides, although its etch rates are slower than for ICP or ECR due to its lower operating pressure.

Effect of additive noble gases in chlorine-based inductively coupled plasma etching of GaN, InN, and AlN

The effects of additive noble gases, He, Ar and Xe to chlorine-based inductively coupled plasmas (ICPs) for etching of GaN, AlN and InN were studied in terms of etch rate and selectivity. The etch rates were greatly affected by the chlorine concentration, rf chuck power and ICP source power. The highest etch rates for InN were obtained with Cl2/Xe, while the highest rates for AlN and GaN were obtained with Cl2/He. It was confirmed that efficient breaking of the III-nitrogen bond is crucial for higher etch rates. The InN etching was dominated by physical sputtering; the GaN and AlN etch rates were limited by initial breaking of the III-nitrogen bond. Maximum selectivities of ∼80 for InN to GaN and InN to AlN were obtained with the Cl2-based discharges.

Reactive ion beam etching of GaAs and related compounds in an inductively coupled plasma of Cl2–Ar mixture

Reactive ion beam etching (RD3E) of GaAs, GaP, AIGaAs and GaSb was performed in a Cl2-Ar mixture using an Inductively Coupled Plasma (ICP) source. `The etch rates and yields were strongly affected by ion energy and substrate temperature. The RJBE was dominated by ion-assisted etching at <600 eV and by physical sputtering beyond 600 eV. The temperature dependence of the etch rates revealed three different regimes, depending on the substrate temperature: 1) sputtering-etch limited, 2) products-resorption limited, and 3) mass-transfer limited regions. GaSb showed the overall highest etch rates, while GaAs and AIGaAs were etched at the same rates. The etched features showed extremely smooth morphologies with anisotropic sidewalls.

Cl2-based inductively coupled plasma etching of CoFeB, CoSm, CoZr and FeMn

Abstract Thin films of CoFeB, CoSm, CoZr and FeMn have been etched in inductively coupled plasma Cl 2 discharges with He, Ar or Xe as the inert gas additive as an additional physical component to the etch process. The etch rates decrease with pressure and go through maxima with rf chuck power and discharge composition. There is a transition from net deposition to etching with increasing source power and rf chuck power, consistent with the need to provide sufficient ion energy and ion/neutral flux ratio to achieve efficient etching of magnetic materials.

Energy band offsets of dielectrics on InGaZnO4

Thin-film transistors (TFTs) with channels made of hydrogenated amorphous silicon (a-Si:H) and polycrystalline silicon (poly-Si) are used extensively in the display industry. Amorphous silicon continues to dominate large-format display technology, but a-Si:H has a low electron mobility, μ ∼ 1 cm2/V s. Transparent, conducting metal-oxide materials such as Indium-Gallium-Zinc Oxide (IGZO) have demonstrated electron mobilities of 10–50 cm2/V s and are candidates to replace a-Si:H for TFT backplane technologies. The device performance depends strongly on the type of band alignment of the gate dielectric with the semiconductor channel material and on the band offsets. The factors that determine the conduction and valence band offsets for a given material system are not well understood. Predictions based on various models have historically been unreliable and band offset values must be determined experimentally. This paper provides experimental band offset values for a number of gate dielectrics on IGZO for nex...

Effect of Inert Gas Additive Species on Cl(2) High Density Plasma Etching of Compound Semiconductors: Part II. InP, InSb, InGaP and InGaAs

The effects of the additive noble gases He, Ar and Xe on chlorine-based Inductively Coupled Plasma etching of InP, InSb, InGaP and InGaAs were studied as a function of source power, chuck power and discharge composition. The etch rates of all materials with C12/He and C12/Xe are greater than with C12/Ar. Etch rates in excess of 4.8 pndmin for InP and InSb with C12/He or C12/Xe, 0.9 pndmin for InGaP with C12/Xe, and 3.8 prdmin for InGaAs with Clz/Xe were obtained at 750 W ICP power, 250 W rf power, - 1570 C12 and 5 mTorr. All three plasma chemistries produced smooth morphologies for the etched InGaP surfaces, while the etched surface of InP showed rough morphology under all conditions.

Selective dry etching using inductively coupled plasmas. Part II. InN/GaN and InN/AlN

Abstract Two interhalogen plasma chemistries, ICl and IBr, have been examined for selective dry etching of InN over GaN and AlN. Maximum selectivities of 55 for InN/GaN and 20 for InN/AlN were achieved with ICl, and 30 for InN/GaN and 14 for InN/AlN, respectively, with IBr. There are two reasons for these results—the relatively high volatility of the InI3 etch product and the lower bond strength of InN relative to the other two binary nitrides. Both interhalogen plasma chemistries appear promising for use in electronic device fabrication.