Dry Etching of Reduced Thermal Budget Borophosphosilicate Glass (BPSG) Using Furnace Anneal the Effect of Phosphorus and Boron Concentration

The effect of phosphorus (P) and boron (B) concentration on dry etching of reduced thermal budget borophosphosilicate glass (BPSG) using furnace anneal was investigated. The BPSG film with different THK and P/B concentration was divided into three kinds type that named by top, middle and bottom, respectively. Moreover, the BPSG film was prepared by sub-Atmospheric chemical vapor deposition (SACVD) and was deposited on bare Si surface. The P and B concentration in film was checked by X-ray Fluorescence Spectrometer (XRF). Post BPSG film stabled more than 2h, rapid thermal processing (RTP) combined with furnace anneal with different anneal temperature (400°C,500°C,600°C) was designed to reduce thermal budget. Finally, the dry etch rate was performed using plasma etching. The correlation between anneal temperature, P and B concentration, as well as dry etch rate was investigated and discussed in this paper. Furnace annealing is one of the major challenges for 3D DRAM architectures, owing to the fact that the overall thermal budget on the one hand increase the diffuse range lead to the die area increase, on the other hand high thermal budget may cause lattice damage. The results of this paper indicate that the dry etch rate of BPSG film increased with increasing B concentration or B/P ratio, while decreased with increasing P concentration or P+B concentration. Nevertheless, the relationship between dry etch rate and furnace temperature is nonlinear. Thus, the dry etch rate of BPSG film can be tunning by adjusting the B or P concentration in film that suffered low temperature anneal. The results also imply that the dry etch rate of BPSG film under 400°C anneal can match with sample under 600°C anneal by slightly adjust B and P concentration. For top film, the B concentration reduce about 0.65% and the P concentration need increase about 2.61%, while the etch rate of middle and bottom film under 400°C anneal well match with samples under 600°C, thus the B and P concentration no need adjust. This investigation proved that the anneal temperature of BPSG film can reduce from 600°C to 400°C, which significantly decreased the overall thermal budget. This finding plays significant influence on the development of 3D DRAM architectures.