Novel Deep SAC Etch Process Technology for Advanced FCRAM

Abstract

As scaling-down of COB type FCRAMTM (Fast Cycle RAM) approaches 0. lum, storage node self-aligned contact (SAC) presents the most critical problem for the integration. Small process window is one of the major problems for a deep SAC etch. By using CxFy based chemistry, a deep SAC etch process with higher SIN selectivity and wider etch stop window were achieved. This is quite beneficial for higher performance of advanced FCRAMTM.Introduction FCRAMTM is widely used in high-speed and low-power data transfer applications. Among Pseudo SRAM products, FCRAMTM provides ultra-high performance with low power and high speed. Because it uses a pipeline action not only for column access but also row access [1,2]. FCRAMTm has highly exacting specifications and unique process requirements, such as high refresh, high transistor performance, low standby current, low resistance and low parasitic capacitance of word lines (WL) and bit lines (BL). To achieve these special demands, a COB DRAM-like structure with novel deep SAC etch technology is needed due to the use of metal word line/bit line for obtaining lower parasitic capacitance, lower resistance and higher cell capacitance.This article describes CxFy based chemistry technology of deep SAC Etch for FCRAM applications. Experiment Two approaches of deep SAC structures for different capacitor schemes were implemented. Figure 1 shows one kind of schematic of the deep SAC process. Figure l.a is after Bit Line patterning, Figure l.b is after Bit Line Spacer formation. After ILD filling and CMP, nitride and top TEOS is deposited for future capacitor loop usage, and then the contact hole is patterned (Figl.c). Figure l.d shows the final cross section after deep SAC etching and PR stripping. It should be noted that every process step performance will affect future deep SAC etch performance and process window. Figure 2 is another process scheme. There is no Top nitride and TEOS deposition before photo patterning.Fig2. The schematic of deep SAC process 2 Based on these two schemes, we performed deep SAC etch experiments. CxFy A and CxFy B were used in the experiments.Within the 2 kinds of process schemes, CxFy A based chemistry has better etch stop margin than CxFy B based chemistry for process scheme 1. However, the bottom CD is small. For process scheme 2, CxFy B based technology can produce larger bottom CD than CxFy A while it also providing good etch stop margin.Therefore, process scheme 2-based chemistry deep SAC etch technology was chosen for the final WAT and CP yield test and produced good results.Results and Discussion There are two major issues which commonly arise in SAC etch. One is etch stop, another is Bit line to SAC short. Figure 3 shows these two issues, prior to etch recipe optimization. 145 S~~~~~|E .I (a)~~~~~~~~~(b):