METHOD OF PLASMA ETCHING DOPED POLYSILICON LAYERS WITH UNIFORM ETCH RATES

摘要

In wafer semiconductor manufacture, a method of etching an arsenic doped polysilicon layer down to a patterned boro-phospho-silicate-glass (BPSG) layer provided with a plurality of openings with an uniform etch rate is disclosed. The method relies on a combination of both system and process improvements. The system improvement consists to hold the wafer in the reactor during the etch process with an electrostatic chuck device to have a perfect plasma environment around and above the wafer. On the other hand, the process improvement consists in the use of a non dopant sensitive and not selective chemistry. A NF3/CHF3/N2 gas mixture with a 11/8.6/80.4 ratio in percent is adequate in that respect. The etch time duration is very accurately controlled by an optical etch endpoint detection system adapted to detect the intensity signal transition of a CO line at the BPSG layer exposure. The process is continued by a slight overetching. When the above method is applied to the doped polysilicon strap formation in DRAM chips, excessive or insufficient etching of the polysilicon layer is avoided, so that the doped polysilicon strap thickness is thus much more uniform, opening to opening, within a wafer.