Precise etch-depth control of microlens-integrated intracavity contacted vertical-cavity surface-emitting lasers by in-situ laser reflectometry and reflectivity modeling

We studied the etch-depth control of 980 nm intracavity contacted vertical-cavity surface-emitting laser (VCSEL) structures with GaAs/AlGaAs distributed Bragg reflectors by in-situ laser reflectometry and reflectivity modeling in SiCl₄/Ar inductively coupled plasmas. Highly accurate etch-depth control can be achieved by counting the number of oscillation peaks in the experimental reflectance signal through the fitting of the reflectivity data calculated theoretically using a transfer matrix method. The fits provide a very good agreement, allowing us to distinguish individual layers precisely and stop the etching at a desired depth. After confirmation of the validity of in-situ dry etch monitoring, this technique was employed in the fabrication of microlens-integrated intracavity contacted VCSELs including composition-graded digital alloy AlGaAs for high precision control of the etch depth in intracavity region. The etch-depth difference between calculated and experimental results was kept below 20 nm, indicating a good etch performance. The spatial uniformity of ~ 5% was obtained over 1 × 1 cm² sample size.