Fabrication and performance of selective HSG storage cells for 256 Mb and 1 Gb DRAM applications

Fabrication of rapid thermal nitrided HSG transformed crown capacitor storage cells incorporating an ultrathin low pressure chemical vapor deposition (LPCVD) Ta₂O₅ and Si₃N ₄/SiO₂(NO) dielectric is proposed. 256 Mb array with HSG crown cells of 0.3 μm diameter×0.6 μm height and 49 A T_eff showed an area enhancement factor of 1.7 (relative to untransformed crown cell). C_min/C_max ratio of >0.95, and capacitance of 16.7 fF/cell is obtained. A measured leakage current density of 0.7 nA/cm² at 1.2 V is reported. Metal-oxide-semiconductor capacitor (MOSCAP) devices with HSG electrodes for 1 Gb application are characterized using capacitance-voltage (C-V) and current-voltage (I-V) analyses. Detailed HSG grain characterization results are presented with correlation to the electrical behavior of the devices. Devices are formed using LPCVD Ta₂O₅ and/or Si₃N₄ dielectric. HSG films formed from 4×10²⁰ atoms/cc phosphorus doped amorphous silicon show depletion in C-V behavior. It is shown that phosphine doping of HSG film is required to avoid depletion. Process selectivity of the UHV/CVD HSG transformation mechanism applied to thermal oxide and nitride field dielectrics is fully explored. Selectivity limits for different types of dielectric are also presented. Effect of critical parameters such as a-Si dopant concentration, HSG incubation time, anneal conditions, and a-Si layer thickness on HSG transformation are discussed for 1 Gb crown cells