an automatic arm. An applied radio frequency (RF) substrate power influences the ion

speed; a higher RF power increases the ion speed and the amount of sputtering,

mechanical etching, which occurs. The microwave power influences the plasma density;

an increase in microwave power results in a more dense plasma with more ionized

particles that will enhance chemical etching. Table 1 summarizes these parameters.

Table 1. General trends of etch conditions when a parameter is increased


 Pa s Sputter Chemical R Vertical
 Parameters Etch Rate
 Etching Etching Sidewalls
Pressure 1 1
Temperature 1
Cl2 Flow 1 1
Ar Flow 1 T T
Microwave
Power
RF Power T 1 1


Chlorine-based plasmas are the most commonly used to dry etch GaAs wafers during

device manufacturing [12]. This is primarily because of the volatility of the chlorides

that are formed by the reaction. Group III chlorides, GaCl2 and InCl2, are suitably

volatile at practical processing temperatures where as Group III fluorides, GaF3 and InF3,

are not, making Cl2 chemistry the preferred choice [3]. It is for these reasons that

chlorine has been selected as the etchant of choice for this research.

 Etch Mechanisms

 From previous research, it is understood that the chemical etching mechanism

leads to a more isotropic etch characteristic, and undercutting, while physical sputtering

leads to a more anisotropic etch (Figure 6). The chemical etch of a material depends on

the reaction between the reactive neutral species (i.e., Cl, Cl2) with the sample.