Ion-implant-enhanced reflow of phosphosilicate glass films

Abstract

Ion implantation has been investigated for lowering the thermal fusion of “reflow” temperature of phosphosilicate glass (PSG) films for VLSI applications. Dry-etched patterns of 0.5 microm thick polysilicon films were coated with 1.0 microm PSG (5, 7 and 9 wt.% phosphorus) by LPCVD, followed by implantation of phosphorus and/or boron, each at 2 × 10 16 ions cm −2 at several different energy levels. Reflow was conducted at 950°C in steam for 30 min. Step angles were measured from SEM cross-sections. Implant dose and energy directly affect the reflow profile of the glass. For PSG with 5 wt.% phosphorus, for example, implantation of phosphorus ions implanted at 140, 160 and 190 keV led to reflow step angles where the lowest value was 34° for the 160 keV energy. Boron ions implanted at 60 keV yielded 51°. However, a combined implant of boron at 50 keV and phosphorus at 160 keV gave an angle of only 47°. Implanted boron is not as effective as phosphorus because it causes less reflow-enhancing surface modification. The combination of phosphorus and boron is not as effective as phosphorus alone. Implanting phosphorus at 140 and 190 keV into PSG with 9 wt.% phosphorus resulted in angles as low as 10°, approaching planarization. Arsenic ion implantation followed by rapid thermal fusion was found to be a viable, although generally less effective, alternative to the phosphorus implantation process. We conclude that ion implantation is a versatile and effective technique for enhancing PSG reflow at a reduced thermal budget.