Hwei Heng Wang

Liquid Phase Chemical-Enhanced Oxidation for GaAs Operated Near Room Temperature

A new chemical enhanced oxidation method for gallium arsenide (GaAs) in liquid phase near room temperature (40°C–70°C) is proposed and investigated. Featureless oxide layers with good uniformity and reliability can be grown efficiently on GaAs without any extra energy source. A relatively high oxidation rate (1000 A/h), about 50 times higher than that obtained during oxidation in boiling water has been realized. Based on the results of X-ray photoelectron spectroscopy (XPS), excellent chemical stability after thermal annealing as well as good chemical stoichiometry have been realized. The oxide was determined to be composed of Ga2O3 and As2O3.

Effects of pH Values on the Kinetics of Liquid-Phase Chemical-Enhanced Oxidation of GaAs

The liquid-phase chemical-enhanced oxidation technique has been demonstrated to be an effective means of growing stable native films on GaAs. The gallium-ion-containing solution results in a fairly high oxidation rate near room temperature. The pH value of the oxidation solution appears to be a dominant factor in the kinetics of oxidation. Due to the enhancement of Ga-containing ca tions in the solution, a window of initial pH values from approximately 4.0 to 4.5 is found to be the optimum pH range for oxide growt h. The pH-incorporated mechanism provides consistent interpretations for the unusual experimental results such as etchback of oxid e thickness and increase of refractive index. In addition, the results of the pH-controlled procedure confirms the proposed role o f pH. According to secondary ion mass spectroscopy profiles, it is found that the increasing As/Ga ratio of the oxide film contributes to the increase of oxide refractive index.

NEAR-ROOM-TEMPERATURE SELECTIVE OXIDATION ON GAAS USING PHOTORESIST AS A MASK

Selective oxidation on GaAs operated at near room temperature, by a liquid phase chemically enhanced method using photoresist as a mask, is proposed and demonstrated. Because of the low temperature and electroless features of the oxidation method, the process is simple, economic and reliable. Good electrical insulating properties comparable with those of thermal oxide have been obtained. According to the results of X-ray photoelectron spectroscopy, the chemistry of the oxide surface is stable after thermal annealing. The thermal stability shows the potential for device fabrication.

Effect of crystal orientation and doping on the activation energy for GaAs oxide growth by liquid phase method

We have investigated the oxide growth kinetics of near-room-temperature liquid phase chemical enhanced oxidation on differently oriented and doped GaAs substrates. Oxidation reactions have been studied by analyzing their activation energies and have been found to depend on the bond configuration of crystal planes. Experimental results indicate that the activation energies are independent of the doping of GaAs. The oxidation rates are dopant selective (n−:p+-GaAs∼4:1 at 30 °C under illumination) and sensitive to illumination (without:with illumination∼1:25 at 30 °C for a n+-doped GaAs). In the oxidation reactions, photogenerated holes are found to play an important role. Finally, we have proposed a mechanism based on the band bending and the carrier transport near the oxide-GaAs interface to interpret the experimental observations.

GaAs MOSFETs fabrication with a selective liquid phase oxidized gate

The N-channel depletion-mode GaAs MOSFETs with a liquid phase chemical enhanced selective gate oxide grown at low temperature are demonstrated. The proposed selective oxidation method makes the fabrication process of GaAs MOSFETs more reliable and self side-wall passivation possible. The fabricated GaAs MOSFETs exhibit current-voltage characteristics with complete pinch-off and saturation characteristics. The 2 /spl mu/m gate-length MOSFETs with a gate oxide thickness of 35 nm show transconductance larger than 80 mS/mm and maximum drain current density of 380 mA/mm. In addition, microwave characteristics with f/sub T/ of 1.8 GHz and f/sub max/ of 5.2 GHz have been achieved from the 3 /spl mu/m/spl times/60 /spl mu/m GaAs MOSFETs.

Surface Oxidation Kinetics of GaAs Oxide Growth by Liquid Phase Chemical-Enhanced Technique

The initial stage of GaAs oxidation by a near-room-temperature liquid phase chemical-enhanced technique has been studied. Based on the experimental results of X-ray photoelectron spectroscopy, a complete model illustrating the chemical composition of the grown oxide film has been established. To clarify the kinetics of oxide growth in a liquid solution in more detail, we have also performed selective oxidation and surface profile measurements. Unusual features of the oxide growth kinetics have been observed by investigating the physical structure of oxide at the edge of mask in the selective oxidation.

A planarized shallow-trench-isolation for GaAs devices fabrication using liquid phase chemical enhanced oxidation process

A new planarized trench isolation technique for GaAs devices fabrication by a liquid phase chemical-enhanced oxidation (LPCEO) method is proposed. The LPCEO-trench-isolation technique can be operated at low temperature with a simple and low-cost process. As compared with conventional mesa isolation, the LPCEO-trench-isolation can provide better planarity and isolation properties. Finally, GaAs MOSFETs fabricated with LPCEO-trench-isolation and selective oxidized gate both by the LPCEO method are demonstrated.

Fabrication of depletion-mode GaAs MOSFET with a selective oxidation process by using metal as the mask

The n-channel depletion-mode GaAs MOSFETs with a selective liquid phase chemical-enhanced oxidation method at low temperature by using metal as the mask (M-SLPCEO) are demonstrated. The proposed process can simplify one mask to fabricate GaAs MOSFET and grow reliable gate oxide films as well as side-wall passivation layers at the same time. The 1 /spl mu/m gate-length MOSFET with a gate oxide thickness of 35 nm shows a transconductance of 90 mS/mm and a maximum drain current density larger than 350 mA/mm. In addition, a short-circuit current gain cutoff frequency f/sub T/ of 6.5 GHz and a maximum oscillation frequency f/sub max/ of 18.3 GHz have been achieved from the 1 /spl mu/m/spl times/100 /spl mu/m GaAs MOSFET.