Wet-Chemical Silicon Wafer Thinning Process for High Chip Strength

Three-dimensional integration (3D) has been developed as an emerging technology in a semiconductor industry [1,2]. Silicon wafer thinning is one of the key techniques for 3D integration with through silicon vias (TSVs). In conventional thinning of silicon wafers, backgrinding has been applied where the backside of a wafer is mechanically ground with a grindstone. However, backgrinding causes micro cracks/grinding traces on the back surface layer of the wafer or defects/damage inside it, resulting in reduced yield and mechanical strength of the wafer/chip. In order to overcome some problems caused by backgrinding, we proposed wet-chemical silicon wafer thinning process using HF/HNO3 solutions [3-4]. By optimizing the component ratio of the solution, we also demonstrated a high etching rate (about 800 μm/min) and a uniformity of 3% for the etched samples (6-8 inch wafers). In this study, the effect of wet-chemical silicon wafer thinning process on chip strength was investigated. For this investigation, we measured the fracture stress of thinned chip and compared the results with those of various wafer-thinning methods (Table 1). The 8-inch silicon wafers were thinned down to 100 μm and were then cut into 10 mm-square chip using a conventional dicing saw. The die fracture stress was measured by the three-point bending test (Fig. 1). The die fracture stress was calculated as