Process and film characterization of low pressure tetraethylorthosilicate–borophosphosilicate glass

The pyrolytic decomposition of tetraethylorthosilicate (TEOS) has been used to deposit highly doped borophosphosilicate glass (BPSG) films. The experiments were carried out in a modified low pressure chemical vapor deposition furnace in the 620–680 °C range at a deposition pressure of 0.5 Torr. Trimethylborate and phosphine together with oxygen were found to be the best dopant source combination. The deposited layers adhere strongly to the quartzware and low particle counts of typically less than 0.2 per cm2 were measured. The thickness uniformity was below ±6%, the dopant uniformity was ±0.1 wt. % over a wafer. If compared to low pressure SiH4–BPSG films, the TEOS–BPSG shows superior step coverage and much higher chemical stability up to dopant levels of about 5 wt. % B, 5 wt. % P. The etch rate behavior in buffered HF corresponds to the trends reported for SiH4–BPSG. The electrical characterization of thin TEOS–BPSG and TEOS–SiO2 layers yielded an electrical breakdown strength in the 7–8 MV/cm range. The glass flow properties (wet and dry ambient) were investigated and found to be very good in the 800–850 °C region. By using a rapid optical anneal system, the required step tapering could be achieved at time/temperature combinations of 40 s/900 °C or 10 s/1000 °C. Detailed infrared studies showed strong interaction among the different oxide absorption bands of the TEOS–BPSG layers.