R. P. H. Chang

HYDROGEN PLASMA ETCHING OF SEMICONDUCTORS AND THEIR OXIDES.

Hydrogen plasmas have been used to etch surfaces of semiconducting materials (e.g., GaAs, GaSb, InP, Si), their oxides, and Si nitride. Using a combination of analytical techniques—spectroscopic ellipsometry, Auger spectroscopy, and scanning electron microscopy (SEM), the etch rates, the surface composition and morphology have been studied. It is demonstrated that the selective etching rate of hydrogen plasma for Si over SiO2 is ∠30, and that for GaAs oxide over GaAs is ∠2. It is also shown that the hydrogen plasma etched (and air exposed) GaAs surfaces have a Ga/As concentration ratio nearly equal to that of the air cleaved GaAs surface. Similar results have also been obtained for GaSb. Hydrogen plasma etched InP shows surface segregation and is rich in In. The etch rates of the semiconductors and their oxides vary by several orders of magnitude from compound to compound as determined from ellipsometry and SEM. It is also demonstrated that scanning ellipsometry can be used to monitor surface etching proc...

Fluorine enhanced plasma growth of native layers on silicon

The plasma growth rate of native layers, such as oxide and nitride, on silicon is enhanced by the addition of fluorine. An increase in growth rate is obtained, and the oxide growth rates on doped and undoped portions of the silicon substrate are substantially the same. The fluorine is typically added by means of a fluorinated compound, typically CF4, comprising 0.01 to 5 molecular percent of the plasma. Lower substrate temperatures, typically less than 600 degrees C., may be used, resulting in less warpage of the wafer and less diffusion of dopants.

Plasma oxidation of GaAs

A new process for plasma oxidation of GaAs has been developed. Oxide films formed by this simple one‐step dry process have amorphous structure, with composition and thickness uniformity better than ±10% over areas ≲1 cm2. They have a gallium‐to‐arsenic ratio of nearly one. The electrical properties (I‐V, C‐V) of the films are such that this process may be useful in device fabrication.

Hydrogen plasma etching of GaAs oxide

Hydrogen plasma has been used to etch native‐grown GaAs oxide on GaAs substrates. It is found that the rate of etching increases with gas pressure (in the range 10–300 μ) and the rf power (in the range 10–400 W) of the discharge. A typical etch rate of ≊20 A/sec can be easily achieved. The selectivity (determined by scanning electron microscopy) of the oxide etch over the substrate is ≊2. An etch mechanism is proposed, and the use of hydrogen plasma for surface preparation of GaAs and the etching of oxides on other semiconductor materials will be discussed.

Instabilities and induced scattering due to nonlinear Landau damping of longitudinal plasma waves in a magnetic field

The matrix elements for nonlinear wave‐particle scattering (nonlinear Landau damping) are obtained in explicit form for electrostatic waves from the Vlasov‐Maxwell equations. The waves are allowed to propagate at arbitrary angles to the magnetic field, and no restrictions are imposed upon the Larmor radius or the frequencies. In the case k⊥≫k‖, the symmetry relations for mode‐mode coupling are demonstrated by appropriate manipulations of the matrix elements. This allows one to cast the nonlinear Landau damping coefficients in a particularly simple form. The conditions for explosive instabilities are obtained, and a possible stabilization mechanism for these instabilities is pointed out. In the limit of either perpendicular or parallel propagation to the magnetic field, a comparison is made with previous results. The nonlinear stability of two types of velocity anisotropy instabilities are examined. Explosive instabilities are found to exist both for Harris modes and upper hybrid loss‐cone modes. In additi...

A new resonant ellipsometric technique for characterizing the interface between GaAs and its plasma‐grown oxide

At certain wavelengths, depending on the thickness of a thin transparent dielectric layer on an absorbing substrate, a standing‐wave condition can be produced that efficiently couples the S wave to the substrate, simulating a cavity resonance in the dielectric and maximizing the complex reflectance ratio. Under these conditions high sensitivity is obtained to the nature of the interface between the dielectric and the substrate. We illustrate the method by applying it to plasma‐oxidized GaAs samples using scanning ellipsometry from 1.5 to 5.6 eV. As‐grown samples exhibit a composite transition layer at the interface consisting of a mixture of oxide, unoxidized GaAs, and elemental As. A crystalline As layer is formed at the interface by annealing in N2 at 550 °C.

The effect of interface arsenic domains on the electrical properties of GaAs MOS structures

Postgrowth annealing of plasma grown GaAs oxides in N2 and H2 result in very different electrical behaviors. By examining cross‐sectioned specimens of these oxides with transmission electron microscopy, and correlating the observed structure with electrical measurements, it is demonstrated that metallic As at the oxide‐semiconductor interface plays a significant role in determining the MOS characteristics.

A new method of fabricating gallium arsenide MOS devices

A new method of fabricating gallium arsenide MOS devices with improved electrical properties is discussed. The device consists of a gallium arsenide substrate overlaid with a gallium arsenic oxide, a thin aluminum oxide, and a metallic contact. The oxide layers are fabricated using a plasma oxidizing process. These MOS devices show very high breakdown voltages (typically ≈±4×106 V/cm) and have low surface‐state densities (≈5×1010 cm−2).

Parametric decay into ion cyclotron waves and drift waves in multi-ion species plasma

Parametric decay processes near the ion cyclotron frequency are investigated experimentally and theoretically in multi‐ion species plasmas. The relevant theoretical dispersion relation of the parametric coupling is derived, including the ion drift motion. Experimental data obtained in the Princeton L‐4 device verify these theoretical predictions in some detail. In a helium‐neon plasma, the relative ion drift motion excites electrostatic ion cyclotron waves (the kinetic ion‐ion hybrid mode) when ω0≳ΩHe +ΩNe. In a region of large density gradient, the ion drift motion also excites low‐frequency drift waves when ω0≳ΩHe+ω*. The experimental data are found to agree well with the theory. The relevance of these processes to ion cyclotron heating of fusion plasmas is discussed.

MULTIPURPOSE PLASMA REACTOR FOR MATERIALS RESEARCH AND PROCESSING.

The operation of the Bell Laboratories large capacity, multipurpose plasma reactor for materials research and processing is discussed. The design of the reactor is such that all the plasma parameters can be independently controlled. This device has been used for growing, deposition, etching, as well as charged‐particle‐beam milling of thin films.