An investigation on ultrathin wafer dicing by ultrafast laser with high density plasma etching

This work includes design of microwave plasma source, ICP chamber, laser scribing trials, development of the water soluble mask material and DRIE process. Electron cyclotron resonance (ECR) plasma sources are used for a variety of materials processing applications such as semiconductor etching and deposition. ECR sources has several advantages over reactive ion etchers (RIE) commonly used since the 1970's, among which are the ability to operate at much lower neutral gas pressures and much higher plasma densities at lower plasma potentials. As it is applied to silicon substrate higher etching rate can be achieved. PVA does not absorbed laser energy at light waves from IR to green spectrum commonly seen in commercial laser. Special chemicals such as 4,4'-dicarboxybenzophenone, benzophenone-4-carboxylic acid, 2-carboxyanthraquinone, 1,2-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid etc. have to be added to increase the optical absorption so that the PVA can be removed by laser. The PVA has certain resistance to plasma etching. In the well calculate time frame the mask can protect the die after the kerfs are completed. An ultrafast (pico-second) laser is used to scribe the wafer. The advantage of applying ultrafast laser is that it can ablate the substrate and also the thin metal (copper) layers embedded in the wafer with ease. However, the depth of laser cut has to be controlled uniformly across the whole plane even if the layer may variate at different locations. This has to done by laser positional synchronized output (PSO).