Generation And Reduction Of Charge Produced By VUV Irradiation In Organosilicate Dielectrics.

摘要

Plasmas, known to emit high levels of vacuum ultraviolet (VUV) radiation, are used in the semiconductor industry for processing of low-k organosilicate glass (SiCOH) dielectric device structures. VUV irradiation induces photoconduction, photoemission and photoinjection. These effects generate trapped and mobile charges within the dielectric film, which can degrade electrical properties of the dielectric. Trapped positive charges are generated when electrons are photoemitted from defect states in the dielectric bandgap. Conversely, photoinjection of electrons from the substrate into the dielectric repopulates the defect states, reducing the number of trapped charges. Based on this, we want to determine how modifications of the dielectric's porosity, the nature of the dielectric-substrate interface and the ultraviolet curing process can be used as control knobs to reduce charge accumulation during processing of low-k SiCOH.;The difference in the time integrals of the photoemission and photoinjection (steady-state) currents determines the number of trapped charges generated during irradiation. Surface potential and C-V characteristic measurements showed trapped positive charges in the dielectric. With increased VUV dose, increases in the surface potential and the shift in flat-band voltage were observed along with hysteresis in the C-V characteristics. The hysteresis indicates the presence of mobile charges in the bandgap.;The amount of charge accumulation in low-k dielectrics depends on factors that affect photoconduction, photoemission and photoinjection. To determine how to reduce the trapped charge in SiCOH, three sets of samples were compared. They are (1) pristine and UV cured SiCOH, (2) SiCOH of different porosities, and (3) SiCOH deposited on different substrates. The number of trapped charges increases with increasing porosity of SiCOH because of charge trapping sites in the nanopores. The dielectric-substrate interface controls charge trapping by affecting photoinjection of charged carriers into the dielectric from the substrate. Also, UV curing changes the intrinsic and photo conductivities of SiCOH which affects the number of trapped charges. Modifications to these three parameters, i.e. (1) UV curing induced charge generation, (2) dielectric-substrate interface and (3) porosity of dielectrics, can be used to reduce trapped-charge accumulation during processing of low-k SiCOH dielectrics.