Smooth sidewall in InP-based photonic crystal membrane etched by N2-based inductively coupled plasma

The etching for InP photonic crystal (PhC) hole structure using Cl-2/BCl3/N-2 and BCl3/N-2 inductively coupled plasmas has been investigated for the fabrication of membrane devices. The addition of N-2 into Cl-2-based plasma is shown to enhance the anisotropic etching and to suppress the sidewall roughness compared to the Cl-2/Ar plasma. The profile verticality of PhC structures is improved by the introduction of BCl3. The smooth sidewalls and the vertical hole profiles are obtained when N-2 ratio (N-2 mass flow rate/total gas flow) is superior to 65%. Positive ion fluxes are measured with the variations of gas flow rates for the plasma characterization. It is found that the addition of N-2 to the Cl-2/BCl3 plasma can cause a decrease in positive ion density when the N-2 ratio is more than 20%. Chemical identification of the InP surface after etching by a N-2-based plasma is characterized by transmission electron microscopy, and no nitrogen element is observed along the sidewalls, which indicates a low probability of surface passivation through N-2. By the time-resolved photoluminescence measurement, free-carrier lifetime of 1400 ps is obtained on InP/InGaAsP quantum wells with PhC structures etched by an inductively coupled plasma Cl-2/BCl3/N-2 plasma, which is beneficial for active devices fabrication. Furthermore, InP photonic crystal membrane defect waveguide with one missing row (W1) is fabricated and shows a low propagation loss value of 25 dB/cm while operating below the air-light line. (c) 2008 American Vacuum Society.