Thermal oxidation of AlgaAs: modeling and process control

Abstract

A simple physical model is developed for the thermal oxidation process of AlGaAs using the continuity equation. The model is based on the principle of oxidant mass conservation. Theoretical calculations are compared with experimental data to a good agreement. The model is then applied to the study of VCSEL batch fabrication. Several control parameters are discussed including AlGaAs layer thickness, aluminum composition, initial mesa size, spacing between two adjacent devices, oxidation time, and oxidation temperature.

Modeling the Lateral Wet Oxidation ofAlxGa1−xAsinto Arbitrary Mesa Geometries

“…The problem of the dynamics of wet oxidation of Al-rich thin layers has been tackled in several works [12,22,23]. Most models assume either planar or circular oxidation 2331-7019/19/11(4)/044067 (8) 044067-1 © 2019 American Physical Society geometries disregarding any anisotropies.…”

“…Contrary to the model developed in Ref. [12], we do not aim at calculating an equation for the front position directly. Instead, we consider the reaction-diffusion dynamics of a two-dimensional field corresponding to the water vapor concentration in which we include an anisotropic reaction term.…”

“…[10] and [11]. With present-day techniques, current apertures with micron-size diameters can be obtained, but they are difficult to control and to manipulate [12]. A better control can be achieved with an optical in situ monitoring [13].…”

Optimal control of AlAs oxidation via digital alloy heterostructure compositions

“…The SL consists of a (0. The straight line corresponds to a normal alloy dependence given in [18] and normalized to the first wafer processed here (sample A).…”

Wet Oxidation Process to Al0.98Ga0.02As Layer for the Vertical-Cavity-Surface-Emitting-Laser Fabrications

“…垂直腔面发射激光器(VCSEL)具有圆形光斑、 小发散角、窄线宽、好的动态单模性、易与光纤耦 合、高可靠性等优势, 近年来在激光照明 [1] 、激光泵 浦、激光加工等领域已经和边发射半导体激光器有 着同等重要的地位 [2] 。进行电流限制和光学限制对 于 VCSEL 器件获取高效率激光输出至关重要, 常 用的方案有环形电极、质子注入型、嵌入型、空气 柱型、选择氧化层等 [3] 。湿法氧化具有工艺简单和 可靠性高的优势, 成为批量制造 VCSEL 中选择氧 化层的关键技术。利用湿法氧化工艺对芯片外延层 中某一层材料组分进行特殊设计, 通过刻蚀的开口 对暴露在外的这层结构进行横向氧化形成电绝缘的 选择氧化层。湿法氧化形成的光电限制孔具有良好 的电限制和折射率导引, 使得 VCSEL 可以实现极 低的阈值电流和较高的电光转换效率 [4] 。 对于 AlAs 或者 x 接近于 1 的 Al x Ga 1-x As 层, 湿 法氧化具有很高的选择性, 并能生成致密、绝缘的 氧化物对载流子进行横向限制, 同时氧化物的低折 射率能提供光学横向限制, 减少光的衍射损耗和散 射损耗, 使得制作极小尺寸和极低功耗的 VCSEL 成为可能 [5] 。但是湿法氧化存在着精确控制氧化孔 径尺寸较难的问题, 且形成的氧化层在后续的高温 过程中易出现分层等不足。氧化层的不稳定性可以 通过预加热处理、适当降低炉温、延长氧化时间及 后退火工艺等方法来解决 [6] , 因此精准控制氧化孔 径对提高 VCSEL 的光电特性尤为重要。 除了 Al 含量对氧化工艺有明显影响外, Al x Ga 1-x As 的湿法氧化对温度也极其敏感, 温度过高会使氧化 速率显著增加, 难以精确控制氧化深度 [7] [8][9] , 有效抑制断层和开裂现象, 氧化完成后 缓慢降温并继续通干燥的 N 2 气直至完全冷却。 图 1 湿法氧化实验的材料结构 [14][15][16] 。 上式求导后可变换为：…”