J. A. Caballero

Patterning of Cu, Co, Fe, and Ag for magnetic nanostructures

Wet and dry etching of thin metallic multilayer structures is necessary for the development of sensitive magnetic field sensors and memory devices based on spin–valve giant magnetoresistance elements. While it is well established that Cu, Co, and Fe are soluble in HNO3 and H3PO4 at room temperature, little effort has been made to investigate selective wet and dry etch chemistries. For example, we find Ag is not etched in H2SO4, HCl, or H3PO4 under conditions where etch rates for the other metals are in the range of 2000–60 000 A/min. Electron cyclotron resonance (ECR) SF6/Ar plasmas provide etch selectivities of ⩾5:1 for Ag over Cu, Co, and Fe, while lower selectivities are obtained with CH4/H2/Ar. Cl2-based plasma chemistries leave significant metal–chlorine surface residues, which can be removed in situ by low ion energy H2 or Ar plasma treatments that eliminate corrosion problems. Cu etch rates in excess of 3000 A/min at 25 °C can be obtained in ECR Cl2/Ar discharges because the high ion flux prevents ...

High rate dry etching of InGaP in BCl3 plasma chemistries

A remarkable increase in InGaP etch rate in electron cyclotron resonance BCl3 discharges is observed as the microwave power is increased from 250 W (etch rate ∼500 A/min) to 1000 W (etch rate ∼8000 A/min). The surface roughness measured by atomic force microscopy decreases from 36 nm at 250 W to 2 nm at 1000 W. The high ion flux incident on the InGaP at high microwave powers appears to remove InClx species by sputter‐assisted desorption and prevents formation of the nonstoichiometric In‐rich surfaces generally observed with Cl2‐based dry etching using conventional reactive ion etching.

Deposition of high-quality NiMnSb magnetic thin films at moderate temperatures

Thin films of the ferromagnetic Heusler alloy NiMnSb, of interest for magnetic multilayer devices because of their predicted half-metallic (i.e., 100% spin-polarized) transport properties, have been successfully deposited by rf magnetron sputtering from a single composite target. A novel combination of low argon gas pressure, low deposition rates, and moderate substrate temperatures (250–350 °C) are shown to result in high-quality, low-roughness polycrystalline films of the C1b-type crystal structure, with thicknesses as low as 100 A, without the need for any post-deposition annealing. The structural properties of these films, determined by x-ray diffraction and atomic force microscopy are presented as a function of deposition conditions. The magnetic properties and resistivity are consistent with bulk MiMnSb, which suggests that they will be effective as spin-polarized conducting layers in multilayer thin-film structures.

Extremely High Etch Rates of In‐Based III‐V Semiconductors in BCl3 / N 2 Based Plasma

Extremely high etch rates of InGaP and InP are observed as N 2 is added to BCl 3 discharges. The etch rates of ∼2.0 μm/min and ∼1.8 μm/min for InGaP and InP, respectively, are achieved at 100°C with 1000 W of electron cyclotron resonance power and -145 V self-bias. Optical emission spectra show increases of intensities for Cl 2 + and Cl + emissions with the presence of N 2 in BCl 3 plasmas as well as an additional BN emission at 385.6 nm. This trend of increasing emission intensity is consistent with the increase of etching rate with BCl 3 /N 2 discharge. A low threshold current, 9.7 mA, InGaAs/GaAs/InGaP ridge lasers with a ridge width and cavity length of 1.4 and 750 μm, respectively, were also demonstrated with this etching processing.

Fabrication of nanometer-sized magnetic structures using e-beam patterned deposition masks

We report on the development of a novel technique designed to study dimensional effects in sputter-deposited magnetic materials and multilayer nanostructures without the need for post-deposition patterning. Wires with widths ranging from 40 to 1000 nm have been deposited on Si wafer substrates through a deposition mask fabricated by e-beam lithography. A bilevel resist masking scheme allows smooth, near vertical sidewall profiles, and the resulting structures can be exposed using a simple lift-off process. This process was used to fabricate test structures of Fe, Cu, and Co which were characterized by scanning electron microscopy, atomic force microscopy, and ac resistivity measurements from 3 to 300 K. While the wire structures are geometrically well defined, transport measurements reveal high crystalline defect densities which must be eliminated to fabricate low-dimensional magnetoresistive structures.We report on the development of a novel technique designed to study dimensional effects in sputter-deposited magnetic materials and multilayer nanostructures without the need for post-deposition patterning. Wires with widths ranging from 40 to 1000 nm have been deposited on Si wafer substrates through a deposition mask fabricated by e-beam lithography. A bilevel resist masking scheme allows smooth, near vertical sidewall profiles, and the resulting structures can be exposed using a simple lift-off process. This process was used to fabricate test structures of Fe, Cu, and Co which were characterized by scanning electron microscopy, atomic force microscopy, and ac resistivity measurements from 3 to 300 K. While the wire structures are geometrically well defined, transport measurements reveal high crystalline defect densities which must be eliminated to fabricate low-dimensional magnetoresistive structures.

Magnetic and magneto-optical properties of NiMnSb thin films

We have developed a simple method to deposit crystalline NiMnSb films from a single-composite target using low-power magnetron sputtering. In this process, the substrate temperature is kept as low as 250°C while retaining bulk-like structural and magnetic properties. Magneto-optical Kerr rotation spectra, closely related to the electronic band structure, are found to be identical over the entire energy range to those previously published for high-quality bulk alloys. This suggests that the half-metallic behavior predicted for the bulk alloys will also be found in the present films.

Dry and Wet Etch Processes for NiMnSb Heusler Alloy Thin Films

A variety of plasma etching chemistries were examined for patterning NiMnSb Heusler alloy thin films and associated Al 2 O 3 barrier layers. Chemistries based on SF 6 , Cl 2 , and BCl 3 were all found to provide faster etch rates than pure Ar sputtering. In all cases the etch rates were strongly dependent on both the ion flux and ion energy. Selectivities of ≥20 for NiMnSb over Al 2 O 3 were obtained in SF 6 -based discharges, while selectivities ≤5 were typical in Cl 2 , BCl 3 , and CH 4 /H 2 plasma chemistries. Wet etch solutions of HF/H 2 O and HNO 3 /H 2 SO 4 /H 2 O were found to provide reaction-limited etching of NiMnSb that was either nonselective or selective, respectively, to Al 2 O 3 .

Magneto-optical properties of sputter-deposited NiMnSb thin films

High-quality thin-film of NiMnSb with the Clb crystal structure can be grown by low-power sputtering, at substrate temperatures as low as 250 °C. Structural and magneto-optical properties of these films are similar to those of bulk material prepared at high temperatures, which suggest that the predicted 100% spin-polarized behavior of NiMbSb may also be found in these films. The magneto-optical Kerr spectra have been measured, and they are found to be very sensitive to the preparation condition. The spectrum of the bulk alloy is closely reproduced only in the case of optimized films. This suggests that, in the optimized case, the electronic band structure is bulklike.

Inductively coupled plasma etch processes for NiMnSb

Plasma chemistries based on SF6, NF3, or CH4/H2 were investigated for inductively coupled plasma (ICP) etching of NiMnSb Heusler alloy thin films. The resulting etch rates were a strong function of ion energy, ion flux, and plasma composition. In SF6/Ar discharges, the etch rates increased from 100 to 300 A min−1 under conventional reactive ion etch conditions to >10 000 A min−1 with the addition of even relatively small amounts (200 W) of ICP source power. The etched surface becomes enriched in Mn under these conditions. In NF3/Ar discharges the etch rates actually decrease as ICP source power is increased, leading to net deposition at either high NF3 percentages or high ICP powers. The etched surface is also enriched in Mn under these conditions, with a Sb-deficient region underneath. In CH4/H2/Ar discharges, the etch rates are slower than with pure Ar and show no evidence of a chemical component in the etch mechanism. Since the etch rates are so high in ICP SF6/Ar discharges, it is necessary to pay car...

Comparison of Cl2 and F2 based chemistries for the inductively coupled plasma etching of NiMnSb thin films

Plasma etching chemistries based on BCl3/Ar, BCl3/H2 and NF3/Ar were studied for patterning NiMnSb Heusler alloys thin films and associated Al2O3 barrier layers in an inductively coupled plasma tool. Using BCl3/Ar discharges, high etch rates (⩾1 μm/min) were achieved either at high source power [(1000 W) or high direct current (dc) self bias (−300 V)] and etch rates showed a strong dependence upon source power, ion energy, and gas composition. Hydrogen addition to the BCl3 created new species (HCl) in the plasma, leading to faster etch rates for NiMnSb than in the case of Ar addition. Selectivities of ⩾8 for NiMnSb over Al2O3 were obtained in BCl3-based discharges. On the other hand, NF3/Ar discharges provided a narrow process window for the etching of NiMnSb and the etch rates were much lower compared to those with BCl3. The surfaces of NiMnSb etched with NF3/Ar was smoother (root-mean-square surface roughness of 1.4 nm measured by atomic force microscopy) than the surfaces produced with BCl3/Ar. In term...