Effect of transport and reaction on the shape evolution of cavities during wet chemical etching

The effect of fluid flow, transport, and reaction on the shape evolution of two-dimensional cavities during wet chemi-cal etching was studied. Finite element methods were employed to solve for the fluid velocity profiles and for the etchant concentration distribution in cavities of arbitrary shape. A moving boundary scheme was developed to track the shape evolution of the etching cavity. In the case of pure diffusion and under mass-transfer control, a mask with finite thickness resulted in significantly better etch factor (etch anisotropy) as compared to an infinitely thin mask, albeit he etch rate was essentially unaffected. With fluid flow past the cavity, the etch rate increased fourfold and the etch factor increased by 40% as compared to pure diffusion, under the conditions examined. In addition, the etch rate, etch factor, and cavity wall pro-files showed a strong dependence on etch time as the cavity aspect ratio (depth/width) increased with time during etching. In the modern microelectronics industry, intricate pat-terns are etched through resist masks into thin films of semiconductors, insulators, and metals. For example, etching patterns of controlled shape and with smooth sur-faces into films of GaAs are important in the fabrication of optoelectronic devices; and etching of Cu vias is commo