Optical monitoring of time-dependent topographies in microfabrication.
Date of Issue2013
School of Mechanical and Aerospace Engineering
The main aim of this project was to develop methodology using existing patented CDH system to monitor time-dependent topographies in microfabrication, particularly in wet chemical etching. To achieve this aim, an actual etch rate was predetermined through experiments and will be used as a reference for real time monitoring of etching experiments. Several samples were placed in 30% wt KOH solution for the stipulated timings. After the etching process, the etch depths of these samples were measured and the average etch rate was found to be 4.74 nm/s. To carry out the real time monitoring of etch depth in wet chemical etching, the CDH system was placed right above the Petri dish where the etching process is taking place. The etching process can then be viewed “live” and the system was able to capture the images of the process instantaneously at the stipulated time intervals. Due to limitations of the system, it is not able to accurately measure any feature of height larger than the wavelength of the light source. Hence, it is not able to measure the exact etch depth at any instant. However, the height difference between the photoresist and silicon dioxide was first measured using the system at the onset of the experiment. During the stipulated time intervals, the height difference was measured again and this time the etch depth can be deduced by comparing to the result obtained at the onset of the experiment. With the etch heights obtained, the etch rates during live etching can then be calculated. The average etch rates obtained through the four live etching experiments are 4.28 nm/s, 5.04 nm/s, 4.81 nm/s and 4.33 nm/s. This means that as compared to the actual etch rate, the live etch rates have a difference of less than 10%. This could be due to the environment settings which cause the KOH solution to vibrate and therefore introducing additional waveforms.
Final Year Project (FYP)
Nanyang Technological University