Improving performance in micromachining of silicon wafer using heat-assisted micro electrical discharge method

Abstract

Microelectrical discharge machining (^EDM) is a non-traditional machining technique that has high potential in the processing of semiconductor materials. This technique can produce complex three-dimensional (3D) shapes without cutting forces, to eliminate the tendency of crack propagation, due to the localized pressure on the workpiece. Additionally, it can also produce high precision and good surface quality machining results. However, this method has only been used to machine highly conductive materials such as metals and highly doped silicon (Si) wafers. While this method is not suitable for undoped or lightly doped Si wafers, increasing the conductivity of the Si wafers requires an additional process and cost. This work aims to investigate the |iEDM performance for machining highly and lightly doped n-type Si wafers with various electrical conductivities. The machining performance was examined on both high- (1-10 Q.cm) and low- (0.001-0.005 Q.cm) resistivity Si wafers by means of a range of discharge energies (DE). The results revealed that the parameters of the electrical resistivity and DE of the |iEDM have a great influence on the Si wafer machining performance, in terms of machining time, material removal rate (MRR), surface quality, surface roughness (SR), and material mapping. The minimum amount of DE required to machine the Si wafer was 5^J for both low and high-resistivity Si, of which the highest MRR of 5.842 x 10- 5 mm 3/s was observed for the low-resistivity Si. On the contrary, the best SR, Ra, of 0.6203 |im was achieved for high-resistivity Si, indicating a higher carbon percentage after the machining process. A novel machining method called heat-assisted |iEDM, which increases the conductivity of the lightly doped Si wafer prior to the machining, was used. A p-type Si wafer was tested, and the machining performance was observed while varying the temperature values of the Si wafers in the range of 30 - 250 °C. The results indicated that increasing the machining temperature contributes to a c o higher MRR, lower tool wear rate and lower SR. MRR of 1.43 x 10- mm /s and a SR of 1.487 |im were achieved at 250 °C. This study is expected to promote the advancement of microelectromechanical systems devices in the electronics field, as well as the ability to achieve a high aspect ratio machining with high surface quality results.