Wet Etching Uniformity Technology Research

Wet etching is still widely used in today’s IC manufacturing. Because it can precisely control the etching amount and lower the loss of raw materials, its role will not be replaced in the future. As process geometries continue to shrink, wet etching uniformity is becoming a bottleneck since its impact on device reliability is becoming more critical. As IC technology is moving towards large wafer size and small device dimensions, maintaining and improving the uniformity of the wet etching process is becoming a hot research topic.At present, wet etching equipments are mainly divided into bench and single wafer machine:bench is an immersion treatment-the silicon is completely submerged in the liquid tank, and the surface is very uniform; single wafer machine is a spray process, the etching uniformity is less uniform since the coverage of chemical on silicon surface is hard to control. This study revealed that low etching rate chemical solution has better etching uniformity.This paper has also found some uniformity-related key factors on current process equipments. The transfer speed is very important for bench machine; in contrast, the rotation speed of wafer and spraying head are the key for single wafer machine. These findings pointed out the limitations of current wet etching process and provide a reference for the future. The paper also discovered that adding a spray and rapid drainage function into de-ionized water cleaning helps prevent secondary etching so as to achieve the purpose of improving the etching uniformity. In addition, too long process time for SCI cleaning can not enhance the cleaning, instead, it will make the silicon surface roughness get worse.In this paper, WAT (wafer acceptance test), CP (chip prober) and RE (Reliability) tests are used to evaluate the uniformity impact. The results showed that WAT is directly related to etching uniformity. However, the relationship between etching uniformity and CP/RE is not significant. The relative large critical device dimensions are most likely responsible for this observation.