Optimization of Wafer-level TTV Using RIE Applied for the Extreme Wafer Thinning

Reactive ion etching (RIE) technology has been widely used in the wafer thinning, which is the key technology in the 3D integration and advancing packaging. The choice of etching gas has a significant effect on the etching rate and total thickness variance (TTV) of silicon. By the optimization of etching gas and gas flow rate, it is found that a stable etching rate of 1.25)tm /min on coupon chip can be obtained when the etching gas is SF6+CF4 +02 with the gas flow rates of 10 sccm, 5 sccm and 10 sccm, respectively. In addition, the wafer edge collapses due to the uneven distribution of the reactive ions at the edge during etching, which also affects the total thickness variance (TTV). Thus, shields at the edge of wafer is introduced in RIE and the shields of Height 1, Height 2, Height 3 and Height 4 (Height 1< Height 2< Height 3< Height 4) and the Gap A, Gap B, Gap C (Gap A>Gap B>Gap C)and no shields between shields and wafer edge are also adjusted. Finally, when the shield with a thickness of Height 2 and Gap C between the shield edge and wafe is used, the total TTV for the wafer with the thickness of 5)tm can be controlled within 2 mu m.