Conventional reactive ion etching (RIE) has generally been used for selective etching of GaAs over AlGaAs. However, there is a great demand for an advanced process with improved uniformity and etch rate, and with a minimal damage for GaAs-based devices. With large scale wafers (150 mm GaAs), the uniformity control is becoming more critical. There has been limited application of high-density plasma (HDP) processing for selective GaAs etching. These HDP reactors include electron cyclotron resonance (ECR) plasma, transformer coupled plasma (TCP) source and 13.56 MHz-based inductively coupled plasma (ICP) sources. Some disadvantages of the high density plasma processing include very high rate and poor selectivity of GaAs over AlGaAs. Two MHz-based ICP processing has been popular for high rate via hole etching and non-selective GaAs etching. We have recently developed an advanced process with a 2 MHz ICP reactor as a new solution for selective etching of GaAs over AlXGa1-XAs, where x ≥ 0.1. The ICP process has been developed especially for production lines to replace the conventional RIE process. The advantages of the ICP process include excellent uniformity (< ± 5 % for 100 mm wafer on an electrostatic chuck), controllable etch rates from 400 to 3000 Å/min, vertical sidewall for a high aspect ratio etching, clean and smooth AlGaAs surface after etching as well as high selectivity (> 50 – 100 : 1). This process is also suitable for processing of damage-sensitive devices. The ICP process has proven to be an excellent process solution for production of GaAs devices and has started to replace RIE techniques. The process can also be applicable for other GaAs-based selective etching with similar results, for example, like GaAs over InGaP and GaAs over InGaAs. These experimental results with the 2 MHz ICP source demonstrate that the ICP equipment can be a superior candidate as a multi-purpose rector for front- and back-side etching of GaAs-based devices.
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