A new in situ sensor for trench depth measurements: the TDM 200

Micro Electro-Mechanical System (MEMS) is a rapidly growing field driven by micro machine devices and components for automotive, medical and industrial system application. To meet the challenge of manufacturing this generation of devices, precise and novel control techniques are required. A new in situ sensor, the TDM 200 for trench depth measurements in micromachining applications is presented. The TDM 200 technology is based on a polarimetric differential measurement between 2 laser beams: one located onto a reference point such as the mask and one located on the trench. This arrangement gives the benefit of the extreme accuracy of non contact ellipsometric measurement at normal incidence and eliminates the need for sophisticated vertical substrate positioning. The integrated CCD camera allows laser beam spots positioning onto the substrate. The simple software interface gives an immediate reading of etch or deposition rates and thickness. Usable for deep silicon etch, this new sensor allows monitoring in real time, both etch rate and depth at Angstroms level accuracy. Due to this absolute measurements, Bosch process for MEMS applications can be easily monitor with no external trigger necessary with other interferometry technique due to the alternate succession of etch and deposition steps. Results have been performed for different silicon etch process such as Bosch process with Oxide or Resist mask. Etch rate variations during the process have been noticed when the trench is etched up to 500 micron.