Dutch researcher Michiel Blauw of the Delft Institute of Microelectronics and Submicrotechnology (DIMES) gained his PhD on January 19, 2004, for work on improved fluorine-based plasma etch of deep, narrow microstructures in silicon. Blauw studied how the plasma reacts with the silicon and how the sidewalls must be treated so as to make the trench as deep and as straight as possible.

Dutch researcher Michiel Blauw of the Delft Institute of Microelectronics and Submicrotechnology (DIMES) gained his PhD on January 19, 2004, for work on improved fluorine-based plasma etch of deep, narrow microstructures in silicon. Blauw studied how the plasma reacts with the silicon and how the sidewalls must be treated so as to make the trench as deep and as straight as possible.

The researcher came up with two ways to improve the profile of the trenches in the Bosch process. During this process, a polymer layer ensures that the sidewalls are not etched by the plasma. However, a thin polymer layer is also deposited onto the bottom of the trench hindering the etch process.

Firstly the researcher added a third plasma pulse to the Bosch-process after the etching and passivation pulses. This efficiently removed the polymer layer from the bottom of the trench. A patent has been granted for this method. Secondly he optimised the passivation pulse used to treat the sidewalls so that no polymer deposition occurred on the bottom of the trenches. This made a maximum depth-width ratio of more than 30 possible.

After a variety of experiments in which he added oxygen to the plasma or deposited a polymer layer, Blauw found an effective passivating technique. A plasma with a high ion-density removes the passivating layer from the surface. He also found that the etch rate as a function of the depth-width ratio can be controlled by tuning the ion-density.

Plasma etching provides considerable advantages for the manufacture of inertial sensors such as accelerometers and gyroscopes. This is because the manufacturing processes for the sensor and the electronics for signal processing are compatible, allowing both parts to be integrated onto a single chip. Furthermore, increasing the depth-width ratio of the etched microstructures considerably improves the integration density and accuracy of these devices.

The research was funded by the STW technology foundation.

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