THERMAL-STABILITY LIMITS OF THIN TISI2 - EFFECT ON SUBMICRON LINE RESISTANCE AND SHALLOW JUNCTION LEAKAGE

TiSi2, the silicide most commonly used for a low resistivity self-alig ned salicide process, must become thinner as the junction depth and po ly-Si gate height decrease so as not to affect junction leakage and ga te work function. The thermal stability of the thinner TiSi2 during th e back-end thermal process cycles, is an important concern. We report on the thermal stability of 300 to 700 angstrom thin TiSi2 on As, P, o r BF2 doped poly-Si to annealing at 750 to 850-degrees-C for 10 to 30 min determined by the increase in the resistance of long 0.3 to 1.5 mu m wide poly-Si meander lines. The increase in line resistance is corre lated with changes in the TiSi2 microstructure. Poly-Si lines less-tha n-or-equal-to 0.5 mum wide with less-than-or-equal-to 500 A TiSi2 incr ease their resistance after annealing at 750-degrees-C, 30 min. 500 an gstrom TiSi2 is stable on >0.5 mum wide poly-Si lines after annealing at greater-than-or-equal-to 800-degrees-C, 15 min. Silicide instabilit y increases the reverse bias diode leakage measured for approximately 1500 angstrom shallow n+ (As + P)/p-well junctions whereas it does not increase diode leakage for approximately 2000 angstrom shallow p+ (BF 2)/n-well junctions. Increasing TiSi2 thickness improves thermal stabi lity. Dopant type and concentration affect the TiSi2 thermal stability through their effect on the TiSi2 thickness (thinner on As doped Si) sintered with a particular Ti sintering process. We use Rutherford bac kscattering spectroscopy, transmission electron microscopy, and scanni ng electron microscopy to correlate the increase in effective sheet re sistance of submicron wide poly-Si lines and the increase in ultra sha llow junction leakage with an increase in roughness for 700 angstrom t hick TiSi2 and agglomeration for less-than-or-equal-to 500 angstrom th in TiSi2.