Polymer Process Produces Deep Holes With a High-Aspect Ratio
Staff -- Semiconductor International, 8/1/1998
Polymer Process Produces Deep Holes With a High-Aspect Ratio
Surface Technology Systems (STS, Newport, Wales) developed an advanced silicon
etch process that allows holes nearly 40 times deeper than their diameter to
be produced with almost vertical silicon walls (9008 ±208 to the surface).
This process is expected to be valuable in meeting the continually increasing
need for precision micromachining in the production of sensors and actuators,
etc.
STS employs a cyclic process that is based on fairly conventional dry plasma etching. However, the sides of the hole or other structure being formed are periodically covered with a layer of polymer that protects the freshly exposed vertical surface at the bottom of the cut against further reaction. The polymer also covers horizontal surfaces, but STS has selected its chemistry so that it is rapidly removed from such surfaces by the plasma etch process. Although the layer of polymer is also eroded on the vertical surfaces, this layer is periodically replaced so that the underlying silicon of these surfaces is not affected by the etching process.
STS reports that an etch rate of 3 mm/min can be obtained with an anisotropy of more than 99%, a vertical smoothness of better than 0.25 mm and a horizontal flatness of better than 0.1 µm.
