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) Ta/sub 2/O/sub 5/ and Si/sub 3/N/sub 4//SiO/sub 2/(NO) dielectric is proposed. 256 Mb array with HSG crown cells of 0.3 /spl mu/m diameter/spl times/0.6 /spl mu/m height and 49 A T/sub eff/ showed an area enhancement factor of 1.7 (relative to untransformed crown cell). C/sub min//C/sub max/ ratio of >0.95, and capacitance of 16.7 fF/cell is obtained. A measured leakage current density of 0.7 nA/cm/sup 2/ 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 Ta/sub 2/O/sub 5/ and/or Si/sub 3/N/sub 4/ dielectric. HSG films formed from 4/spl times/10/sup 20/ 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.