Formation and properties of roughened poly-Si electrodes for high-density DRAMs

A novel structure, based upon phosphorus-implanted poly-Si films treated with phosphoric acid (H3PO4) and the standard RCA cleaning process, has been demonstrated as the bottom electrodes of DRAMs(1) stacked capacitors. After the H3PO4 treatment and the RCA cleaning process, micro-islands are formed on the poly-Si surface of the electrodes. For the capacitors with this novel structure, the capacitance value is 18.17 fF/mu m(2) and the effective oxide thickness is 18.9 Angstrom in comparison with conventional capacitors of 5.77 fF/mu m(2) and 59.5 Angstrom. The roughened poly-Si electrode can achieve a surface enlargement of 3.15 times. The leakage current density at +1.65V and -1.65V are 7.24 x 10(-8) A/cm(2) and -3.31 x 10(-8) A/cm(2), respectively, fulfilling the requirements of 256Mb DRAMs. Weibull plots of time-zero-dielectric-breakdown (TZDB) characteristics under ramping voltage test also show tight distribution and good electrical properties. It indicates that the phosphorus-implanted poly-Si films etched by H3PO4 and then cleaned with the standard RCA process can easily and simply increase the surface area and have good electrical properties fulfilling the requirements of 256Mb DRAMs and beyond.