Application of plasma etching to via hole fabrication in thick GaAs substrates

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Abstract
Several aspects concerning the production of via holes in thick (200 μm) GaAs wafer have been investigated. Various halogen containing gases (CCl2F2, SiCl4, BCl3, and CF4) and mixtures of these gases with argon have been characterized for etching rate and isotropy: For etch pressure (13 Pa≤P≤40 Pa), rf power densities (0.7 W/cm2≤rf≤1 W/cm2), rf peak voltages (70 V ≤Vrfp≤300 V), total gas flow rates (20 sccm≤F≤70 sccm), substrate temperatures (60 °C≤T≤80 °C), and etch rates (0.3 μm/min≤ER≤3 μm/min) were observed. Several mask materials (SiO, SiN, Ni, and Al) were tried, with SiO, SiN and Ni giving good results. Well defined V-shaped hole profiles, due to crystallographic etching, were obtained with a 40% CCl2F2/60% Ar gas mixture. Finally, the etch rate of this mixture demonstrated Arrhenius behavior over the substrate temperature range, 50 °C≤T≤240 °C, with an apparent activation energy (Ea) of 0.05 eV, thus allowing useful etch rate enhancement at elevated substrate temperatures.

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