DRY ETCH INDUCED SURFACE DAMAGE AND ITS IMPACTS ON GaAs SCHOTTKY DIODES

Hong Shen, Peter Dai, and Ravi Ramanathan, Skyworks Solutions, Inc., 2427 Hillcrest Drive, Newbury Park, CA 91320

Keywords: GaAs, Schottky diode, dry etch, surface damage

Dry etch plays a very important role in fabrication of modern III-V compound semiconductor devices, based on technologies such as HBT and MESFET. Compared to conventional wet chemical etch, dry etch, which uses reactive gas plasma to remove substances chemically, has many advantages, such as better controllability, higher pattern reproducibility, and lower cost. However, it is well known that dry etch can induce surface damages that will affect physical and electrical properties of devices. These damages include surface roughness due to ion bombardment, surface contamination due to polymer deposition, and surface stoichiometry change due to preferential etching. Highly damaged surfaces in III-V compound semiconductor device manufacturing are least needed since these surfaces are not reproducible, causing high degree of non-uniformities from device to device, wafer to wafer, and lot to lot.

Lam Research 490 plasma etch system is a parallel plate plasma etcher in which the reactive gases come out of a shower head and are converted into plasma by applied RF power on the top electrode. A GaAs wafer sits on the bottom electrode plate which is connected to ground. The reactive gases are a mixture of CF4/CHF3/O2. By design, the ion bombardment is minimal in such a system. Most surface damage is induced by fluorine ions chemically etching the GaAs surface, polymer dumping during etch, and surface oxidation. When a Schottky contact area is opened by this dry etch process, surface states caused by plasma damage will likely impact electrical characteristics of the Schottky diode, such as its effective barrier height, turn on voltage, leakage current, and breakdown voltage. There are many parameters in the LAM490 system which can be changed to influence the fluorine plasma formation and subsequent chemical etch, such as RF power, pressure, gas flow, and electrode temperature. Obviously, questions such as whether the surface damage can be removed by subsequent cleaning steps or heat cycles in following processes still remain. The paper will show that by comparing the barrier height extracted from a large area Schottky diode, the GaAs surface damage can be characterized in terms of different dry etch parameters so that future dry etch processes can be optimized to produce the desired patterns on GaAs, while minimize the GaAs surface damage to a certain extent.

Paper 6a.3.pdf