Warpage-Free Ultra-Thinning Ranged from 2 to 5-um for DRAM Wafers and Evaluation of Devices Characteristics

An ultra-thinning down to 2.6-um using 300-mm 2Gb DRAM wafer has been developed. Effects of Si thickness and Cu contamination at wafer backside in terms of DRAM yield and retention characteristics are described. Total thickness variation (TTV) after thinning was below 1.9-um within 300-mm wafer. A degradation of retention characteristics occurred after thinning down to 2.6-um while no degradation after thinning down to 5.6-um for both wafer and package level test were found. In-depth analysis such as stress variations and distributions, and behavior of Cu diffusion from the back side of ultra-thinned DRAM wafer are evaluated using by TEM, EDX, TOF-SIMS, Positron annihilation spectroscopy (PAS), and μ-Raman spectroscopy.