In-situ control of deep silicon etch
The aim of the non-exclusive collaboration is to characterise and develop further the capabilities of STS' ASE technology and Jobin Yvon's TDM200 integrated metrology product. The introduction of the Jobin Yvon TDM200 system promises improved efficiency in MEMS manufacturing by eliminating the need to monitor tool performance using test wafers and by ensuring repeatable device performance.
The TDM200 is an on-line tool that can be used to depth target deep trench etches produced by the Bosch Process. The tool uses a patented twin-spot interferometric camera combined with ellipsometry to measure the trench depth from the phase shift generated between two laser spots. One laser spot is positioned on the mask and the other on the trench.
The system does not require etch / deposition synchronisation signals from the etcher, and measures the depth directly, rather than inferring it from the etch rate, as is required for traditional interferometry based tools. This allows processes using the shortest etch cycles to be controlled.
The work at STS has aimed at enabling control of the etching process 'in situ' to depths in the region of 500microns, some ten times deeper than conventional methods. Potential applications include 3D interconnects, inkjet heads, and pressure sensors.
Andrew Chambers, technology director at STS, comments: "Current technologies can only monitor up to 50 micron using a switched process. Any deeper and alternative techniques become less reliable. With this solution, the depth to which we can confidently work is significantly increased with no intrinsic limitations. We can monitor etch depth in real time and, ultimately, the savings in both time and money are significant."