Gerhard Franz

Dry Etching of III/V ‐Semiconductors: Fine Tuning of Pattern Transfer and Process Control

Progress in dry etching processes [reactive ion etching (RIE) and electron cyclotron resonance etching, (ECRE)] is described, concerning etch geometry and fidelity of pattern transfer by using advanced techniques to produce masks of photoresist and Al 2 O 3 or SiO 2 . In contrast to capacitively coupled hydrogen/methane discharges, in which the etch rate of GaAs is significantly lower than that of InP, in ECR discharges by the simple variation of the gas composition, the etch rate of GaAs can be driven to values comparable with InP The different on-line monitoring techniques are compared. It is shown that optical emission spectroscopy can be applied successfully even with sample areas of about 2 cm 2 at etch rates of 50 nm/min.

Extremely Low Contact Resistivity of Ti/Pt/Au Contacts on p + ‐ InGaAs as Determined by a New Evaluation Method

A convenient method for determining a low contact resistivity ρ c is described and experimental results are presented. Small dots of p + -InGaAs on a thick and highly conductive substrate are metallized. The corresponding boundary problem of the current distribution is solved by using an integral equation which can be evaluated numerically. This method can be used to obtain ρ c from experimental data. The procedure overcomes the difficulties usually encountered with the transmission line method since the inhomogeneity of the current density under the contact dots is fully taken into account

Anodic oxidation of InP using a citric‐acid‐based solution

An electrolyte for anodic oxidation of InP is described which takes into account the extreme sensitivity of its native oxide to water. It is an aqueous solution of citric acid buffered to nearly neutral pH and highly diluted by glycerine or ethylene glycol which can produce smooth native oxide films on InP. The breakdown field is about 3.5×106 V/cm. Nearly no shrinkage even at temperatures up to 590 °C has been observed indicating that the oxide is very densely packed.

Comprehensive analysis of chlorine-containing capacitively coupled plasmas

Capacitively coupled discharges of strongly reactive atmospheres containing mixtures of boron trichloride (BCl3) and chlorine (Cl2) are investigated employing spatially resolved Langmuir probe measurements, and three probes that are spatially integrating methods: optical emission spectroscopy (OES), self-excited electron resonance spectroscopy (SEERS), and impedance characteristics of the discharge. The analysis covers the pure gases including some mixtures, discharge pressure, and rf power over nearly two orders of magnitude, and their impact on important plasma parameters of “first order,” such as plasma density, plasma potential, electron temperature, temperature of the plasma bulk, electron collision rate with neutrals, and actual rf power coupled into the discharge. From these, other properties (electrical conductivity, capacitance, plasma bulk resistance, sheath resistance, and its electrically defined thickness) can be derived. Since the methods are partially complementary, a mutual control of the obtained data is made possible, and we finally obtain a self-consistent model for capacitive coupling connecting data obtained with electrical and optical probes. Compared to electropositive discharges of inert atomic gases (Ar) and molecular gases (H2), which are used as calibration standard for BCl3 and Cl2, the electron plasma density ne is definitely lower, whereas the electron temperature Te is significantly higher, which would be expected by electron attachment to the electronegative molecules—at least at higher discharge pressures. Furthermore, we compared values for Te and ne obtained with OES and SEERS, respectively, and with the Langmuir-probe system. The agreement in electron plasma density and electron temperature for Ar is surprisingly good, despite the fact that the electron energy distribution would be described with two temperatures. For argon plasma, the variation of the calculated dc conductivity for nearly pure capacitive coupling either from impedance measurements or SEERS is within 30%. This is a result of uncertainties in current path rather than principal faults of the various methods. For the reactive, molecular gases, however, the results vary significantly. These data serve to determine several derived properties. Among these, are the sheath thickness, which is compared with optical and electrical data, and the conductivity of the plasma bulk. As they are derived from simultaneous, but independent measurements, they confirm the relative simple model of an electropositive discharge (argon and argon/krypton), and stress the difficulty to describe plasmas consisting of electronegative constituents (Cl2, BCl3, and their mixtures) which is due mainly to a pressure-dependent transition from stochastic to ohmic heating and from electropositive to electronegative behavior.Capacitively coupled discharges of strongly reactive atmospheres containing mixtures of boron trichloride (BCl3) and chlorine (Cl2) are investigated employing spatially resolved Langmuir probe measurements, and three probes that are spatially integrating methods: optical emission spectroscopy (OES), self-excited electron resonance spectroscopy (SEERS), and impedance characteristics of the discharge. The analysis covers the pure gases including some mixtures, discharge pressure, and rf power over nearly two orders of magnitude, and their impact on important plasma parameters of “first order,” such as plasma density, plasma potential, electron temperature, temperature of the plasma bulk, electron collision rate with neutrals, and actual rf power coupled into the discharge. From these, other properties (electrical conductivity, capacitance, plasma bulk resistance, sheath resistance, and its electrically defined thickness) can be derived. Since the methods are partially complementary, a mutual control of the ...

Reactive ion etching GaAs and AlAs: Kinetics and process monitoring

The BCl3/(Ar,He) etching process for AlGaAs layers is described and analyzed. It was thoroughly investigated whether the mechanism of plasma etching could be evaluated using the loading effect. Very smooth sidewalls of the structures were obtained with using an optimized process to treat the photoresist after its development. It is shown that various end point detection methods can complement each other and enable etch depth monitoring with a depth resolution of significantly better than 50 nm at a total depth of more than 2.5 μm.

Electron heating in capacitively coupled discharges and reactive gases

The effective collision frequency νeff of electrons in capacitively driven discharges of Ar∕Kr, Cl2 and BCl3 has been investigated using self-excited electron resonance spectroscopy. The most prominent features are the steep increase of νeff at low power inputs in all three gases and a slight but systematic decrease of νeff versus p for Ar∕Kr and BCl3 over the whole pressure range investigated. At medium pressures, the effective collision rate νeff in Cl2 increases by 2 orders of magnitude which is a clear manifestation for the transition from stochastic to ohmic heating. These features have been correlated with data gained with a V(I) probe. The dependence of the ohmic discharge resistance is mainly determined by the drastic change of νeff rather than by the variation of electron density ne.

Characterization of sputtered indium tin oxide layers as transparent contact material

The electrical, optical, and various mechanical properties of rf sputtered indium tin oxide layers were investigated in terms of electrical resistivity (four-probe measurement and Hall), optical transparency, scanning transmission electron spectroscopy and x-ray spectroscopy. Whereas the specific conductivity is at the lower limit reported in the literature (2×10−4 Ω cm), and the optical transparency is as high as 90% in the wavelength range between 550 and 800 nm, the grain size is between 10 and 25 nm. The stress is tensile and in the range of 7 kbar after deposition, to drop to 3 kbar after anneal.

Improved shallow p+ diffusion into InGaAsP by a new spin‐on diffusion source

Shallow p+ diffusion into InGaAsP (λ=1.3 μm) has been improved by employing a new spin‐on source based on Zn‐doped alumina. Thereby the thermal expansion coefficients of diffusion source and semiconductor are better matched together than in case of the more common Zn‐doped silica films. Consequently, besides an excellent mechanical stability of the spin‐on films over a wide temperature range, the influence of mechanical stress on the diffusion process is effectively reduced. Applying diffusion temperatures around 600 °C surface hole concentrations above 6×1019 cm−3 and extremely low specific p‐contact resistances of 2–3×10−6 Ω cm2 have been achieved.

Sidewall passivation of GaAs in BCl3-containing atmospheres

The sidewall passivation of GaAs in atmospheres containing the chain-building molecule BCl3 has been investigated employing Auger electron spectroscopy and time-of-flight secondary ion mass spectrometry. It could be proven that the film that protects the sidewalls from further chemical attack is composed mainly of (B2Cl4)∞ rather than polymers of B2O3.

Evaporation and thermal cracking of dimeric parylenes

The common industrial technique for the deposition of coatings of polyparylene on three-dimensional substrates is the so-called Gorham method, which makes use of thermally cracked, dimeric precursors that form a polymeric film on a cold substrate. Although this method is easily applied, it is still a challenge to coat surfaces with thin, homogeneous layers less than 1 μm in thickness since mass flow controllers cannot be applied. To overcome this deficiency, several methods have been developed. The authors present here a new technique which allows sudden starts and stops simply by variation of the chamber pressure with an inert gas. Moreover, deposition of reproducible, precise layers of polymeric parylenes requires knowledge of the vapor pressures of the dimeric precursors, the equilibrium for the dissociation into monomers, and the flow of dimers into the reactor. Two straightforward manometric methods are used to measure the vapor pressure, whereas the equilibrium is measured by mass spectrometry. The ...