V J Law

Chloromethane-based reactive ion etching of GaAs and InP

A process for reactive ion etching of GaAs and InP is described using a mixture of ClCH3/X, where X=H2, He, O2, Ne or Ar. The ClCH3/H2 process is shown to etch GaAs and InP with anisotropic etch rates of up to 80 and 300 nm min-1, respectively. For the ClCH3/O2 process an etch rate of 11 nm min-1 is obtained for GaAs with no appreciable etching of InP. This simple combination of gases leads to the realization of selective InP over GaAs or GaAs over InP etching. When compared with CH4/H2 RF plasma etching in the same reactor, a significant reduction in the measured applied RF power density and self-bias is observed.

Reactive ion etching of GaAs using CH4: in He, Ne and Ar

RF-plasma reactive ion etching of GaAs using a dilute mixture of methane in helium, hydrogen, neon or argon is described. The process is shown to etch GaAs at rates up to 60 nm min-1 for CH4:Ar, with a high degree of anisotropy. Results show that etch rates scale with the substitution of He

Substrate temperature dependence of GaAs etch rates in CH4:H2 MORIE

The dependence of GaAs etch rates on cathode temperature has been investigated in the range of 285-365 K for a CH4:H2 RF plasma. Results indicate that the apparent activation energy Ea, is strongly influenced by the CH4 partial pressure. GaAs etch rates have an activated temperature dependency with measured values of Ea, varying from approximately=0.7 eV in H2 down to approximately=6.5 meV under high CH4 partial pressures. Thus GaAs etch rates become progressively independent of temperature with increasing CH4 partial pressure. Consequently etch rate stability is enhanced at high CH4 partial pressures, thereby enabling reproducible deep mesa etching.

Plasma etching of GaAs and AlGaAs using 300 kHz and 13.56 MHz excitation frequency

A pulse-plasma etch process for GaAs and Al0.3Ga0.7As at 300 kHz and/or 13.56 MHz excitation frequency using a gas mixture of ClCH3/H2 is reported. The plasma etching is performed using a reactive ion etch (RIE) reactor combined with an external helical RF coil. The GaAs over Al0.3Ga0.7As etch selectivity is investigated as a function of driven electrode frequency and duty cycle. The addition of a capacitive coupled plasma driven by an external RF coil is also investigated. In the normal RIE configuration but at the 300 kHz excitation frequency, the GaAs etch rate is found to be greater than at 13.56 MHz, although the GaAs over Al0.3Ga0.7As etch selectivity (3:1) is not altered. These results illustrate the effect of plasma excitation frequency either side of the ion transition frequency ( approximately 2 MHz). The use of the external RF coil is found to increase the GaAs over Al0.3Ga0.7As etch selectivity to 10:1. The etch process is interpreted as a competitive etch-deposition process which is controlled by the ion/radical flux at the semiconductor surface.

ECR/magnetic mirror coupled plasma etching of GaAs using CH4:H2:Ar

A study of CH4:H2:Ar microwave ECR-plasma etching of GaAs is presented. GaAs etch rates are measured as a function of the constituent gas flow rates, applied RF and microwave powers, substrate temperature and magnetic-table separation. The results indicate that for CH4:H2:Ar ECR etching of GaAs, etch rates of 25 nm min-1 can be achieved. The electrical damage in a GaAs/AlGaAs HEMT Hall bar structure was investigated by etching off the GaAs capping layer. Results indicate that ECR-plasma etching with an additional RF-table bias in the range of -40 to 0 V does not significantly increase the source-drain resistances, measured at 300 K, to that of a wet etched sample. Some degradation in n and mu was found at 1.2 K.

Chloromethane-based reactive ion etching of III–V semiconductor materials

Abstract This paper describes rf plasma reactive ion etching of Al 0.3 Ga 0.7 As, GaAs and InP semiconductors using a mixture of ClCH 3 /X, where X = H 2 or O 2 at a chamber pressure of 2.0 Pa. The ClCH 3 /H 2 process is shown to produce smooth anisotropic etch rates of: 30 nm min −1 for Al 0.3 Ga 0.7 As, 80 nm min −1 for GaAs and 300 nm min −1 for InP at an applied rf power density of 1.3 W cm −2 . GaAs etching with the substitution of H 2 for the noble gases He, Ne or Ar indicates that the etch reaction is controlled by the ionization efficiency of the admix gas. For the ClCH 3 /O 2 process, a GaAs etch rate of 11 nm min −1 is obtained with no appreciable etching of Al 0.3 Ga 0.7 As or InP. At a rf power density of 0.6 W cm −2 both ClCH 3 /H 2 and ClCH 3 /O 2 mas produce an etch stop on Al 0.3 Ga 0.7 As whilst etching GaAs. Optical emission spectroscopy of ClCh 3 /H 2 plasma etching of GaAs and InP shows that the 417.2-nm and the 451.1-nm In optical emission lines can be used to monitor the GaAs and InP etch rates.

Optical emission spectroscopy of plasma etching of GaAs and InP

Abstract This paper describes optical emission spectroscopy between 260 – 800 nm for CICH 3 /H 2 rf-plasma reactive ion etching of Al 0.3 Ga 0.7 As, GaAs and InP compound semiconductors. The optical emission species identified for GaAs and InP etching are: Ga, GaCl, In, InCl and diatomic P 2 (A 1 II g -X 1 Σ + u ) and P 2 + (C 2 II-X 2 II) lines. Under the plasma condition used here and allowing for the stoichiometry of the etch species, it is found that the ratio of emission intensity is Σ(In/P) ≈ 1.4. Taken together with the disparity between In and P 2 vapour pressures, these results suggest that the initial rate of Indium desorption is a factor 1.4 greater than that of phosphorous, suggesting a near-surface P-enriched surface.

Propane: hydrogen MORIE of GaAs

Metal-organic reactive ion etching of GaAs and related III-V semiconductor materials, using an RF plasma containing a mixture of C3H8:H2 is described. The kinetic properties of the process are compared with CH4:H2 and C2H6:H2 etching of GaAs. Results indicate that when the H2 flow dependency is optimised, C3H8:H2 produces between 20-38 nm min-1 GaAs etch rates, with a reactivity of 2.5 greater than CH4:H2 RF plasmas.

Loading effects in CH 4 and H 2 MORIE of GaAs

Abstract We report on GaAs area loading effects associated with CH 4 :H 2 rf plasmas. The results highlight the importance of area loading and reactivity of both optical and electron beam resists when etching GaAs structures. 1, the GaAs etch rate is inversely proportional to the exposed GaAs surface area. 2, Organic photoresists play an active role in the plasma etching process, to an extent that GaAs etch rates become dependent on the selective reactivity of the competing reactions of both GaAs and photoresist. At elevated cathode temperatures, i.e. above ≈340K, plasma-photoresist reaction becomes significant when performing an Arrhenius analysis. We have also observed significant HRN e-beam resist loading for free standing GaAs structures with varying array spacing.