SELECTIVE POLYCRYSTALLINE SILICON GROWTH AND ITS APPLICATIONS TO TRENCH ISOLATION

A selective low temperature polycrystalline silicon growth process has been developed and applied as a dielectric isolation technology to ov ercome the drawbacks of local oxidation of silicon (LOCOS) for high pe rformance VLSI circuits. By selectively depositing polycrystalline sil icon in nitride-lined trenches using the SiCl4/H2 system, comparativel y planar dielectric isolation regions were created upon subsequent oxi dation. Oxide-masked test wafers with variable width trenches were use d to exhibit selective polysilicon growth within a production chemical vapor deposition (CVD) reactor. Independent process parameters consid ered for selective growth optimization included prebake temperature, t otal reactor pressure, reactor temperature, wafer cleaning procedure, and in situ surface pretreatment procedure. The dependent response var iables included surface morphology or planarity, crystallinity, select ivity, and growth rate. X-ray diffraction, scanning electron microscop e (SEM), and transmission electron microscope (TEM) were used to chara cterize deposition layer surface morphology and crystallinity. A filte red dilute HF etch combined with a 975-degrees-C, 50 Torr H-2 prebake effectively removed native oxides and left the surfaces relatively fre e of foreign matter detrimental to selectivity. Selectivity of approxi mately 2 particles/mm2 was achieved using this surface preparation tec hnique within a class 1000 clean room. Furthermore, a N, pretreatment of the surface at 800-degrees-C promoted polycrystalline deposition wh en followed by a 700-degrees-C, atmospheric SiCl4/H2 growth step. This investigation has led to a multiple-step selective polysilicon growth (SPG) process which is repeatable and robust to normal laboratory var iations. Advanced bipolar devices isolated by oxidized selective polys ilicon trench refill have exhibited leakage currents of only 4.3 pA at a tub-to-tub voltage of 20 V Trench dimensions isolating the active t ubs were 2 mum deep, 1 mum wide, and 10 mum long.