Plasma Etching

Three dry etch systems are available in the MFL. The most sophisticated of these systems is a PlasmaTherm SLR-772 ECR etcher with cryogenic substrate cooling to -130° The ECR system allows independent control of the plasma excitation power (provided with a 700 W 2.45 GHz microwave source) and average ion bombardment energy at the substrate (controlled by a separate RF bias source). Wafers up to 150 mm in diameter can be loaded in this system, but the zone of uniform etching is only 100 mm in diameter. The system is pumped with an Alcatel 5900 CP turbopump. The PlasmaTherm SLR-772 is dedicated to polysilicon gate etching. Using an SF6 chemistry, 0.2 µ long polysilicon gate MOSFETs have been produced with this system. Lithography for the latter experiment was provided by the Focussed Ion Beam facility of NRC. A Cl2 gate etch process is presently being developed.

An MRC RIE 61 diffusion-pumped reactive ion etcher is used for oxide etching, including sidewall spacer formation. CHF3 is used as a source gas for this system. As an illustration of the capabilities of this system, vertical- walled optical waveguides 10 æm high have been etched in deposited SiO2 layers to form optical waveguides.

A simple Technics Planar Etch II tabletop planar plasma etcher is available for general-purpose dry etching. This system is mechanical pumped with a base pressure of about 20 mTorr, and so is not suitable for reactive ion etching. It is used with CF4/O2 chemistry for polysilicon and silicon nitride etching when precise pattern control is not required, and with oxygen chemistry to etch polyimides and other organics.