Influence on the long-term stability of polysilicon resistors from traces of titanium and tungsten

Trace amounts of a residue, formed during patterning of the TiW film by etc hing in H2O2, cause a significant improvement in the long-term stability of polysilicon integrated circuit resistors. The stabilization is the result of a reduction in the amount of hydrogen reaching the grain boundary dangli ng bonds during processing. This appears to be due to a retardation in the diffusion of hydrogen caused by an ability of the TiW residue on the boroph osphosilicate glass surface to change the relative amounts of atomic and mo lecular hydrogen. The amounts of hydrogen involved in the resistivity chang es have been evaluated. Typically, for 500 nm thick 5 x 10(14) cm(-2) boron -implanted chemical vapor deposited polysilicon films with a grain size of 150 nm, the concentration of grain boundary traps was 3.8 x 10(12) cm(-2). The amount of hydrogen passivating dangling bonds after hydrogen annealing and plasma-enhanced chemical vapor deposition nitride passivation was 5.9 x 10(11) cm(-2). After a 1000 h electrical and thermal stress at 150 degrees C saturated the resistance drift, the amount of hydrogen that left the dan gling bonds was 4.5 x 10(10) cm(-2). The presence of TiW residue reduced th e amount of hydrogen reaching the dangling bond by 1.3 x 10(11) cm(-2) and that leaving after stressing by 1.8 x 10(10) cm(-2) (C) 2000 The Electroche mical Society. S0013-4651(99)09-041-2. All rights reserved.