Nature of D-defects in Czochralski single crystal silicon

The nature of D-defects in Czochralski single crystal silicon, including the morphology, dissolution thermodynamic/kinetics, and electrical behavior has been investigated. For wafers with a D-defect density of {dollar}{lcub}approx{rcub}1times10sp5{dollar}cm{dollar}sp{lcub}-3{rcub}{dollar}, the D-defect related oxide breakdown voltage increases with oxide thickness up to {dollar}approx{dollar}1000A{dollar}spcirc{dollar} and then recovers with further increases in oxide thickness. A one-to-one correlation of the D-defect induced breakdown site with cross-section TEM via MOS/EBIC and FIB clearly exhibits that D-defects are cavities of 0.25 to 0.50{dollar}mu{dollar}m in diameter, which induce large variation in oxide thickness around the defect site. In addition, the D-defect induced oxide breakdown is associated with resolved shear stresses at the defect site.; After a dry oxidation at 1200{dollar}spcirc{dollar}C for 2hrs, the D-defect density decreases with depth from the surface up to some critical depth, determined by the injection rate of interstitial silicons, and then increases toward that in as-grown wafer. During oxidation, the profile of the D-defect density exactly follows that of the vacancy concentration, which indicates that the driving force for the D-defect dissolution is vacancy undersaturation caused by annihilation between injected interstitial silicons and vacancies in the matrix. The D-defect profile evidently demonstrates that the D-defect nature is vacancy related defect, vacancy agglomerate. The D-defect dissolution improves B-mode type of oxide breakdown failures for t{dollar}sb{lcub}rm ox{rcub}approx{dollar}1000A{dollar}spcirc{dollar} and is a function of the injection rate of interstitial silicons. Although the presence of D-defects does not influence time zero oxide breakdown of {dollar}approx{dollar}170A{dollar}spcirc{dollar}, it degrades the time dependent dielectric oxide breakdown characteristic, which is associated with oxidation induced resolved shear stresses.; D-defects and oxygen precipitates exhibit different oxide breakdown dependencies on oxide thickness. For oxygen precipitates, oxide degradation initially increases for t{dollar}sb{lcub}rm ox{rcub}{dollar} up to {dollar}approx{dollar}190A{dollar}spcirc{dollar} and then decreases with increasing t{dollar}sb{lcub}rm ox{rcub}{dollar}. TEM observations of oxide breakdown site show that polyhedral oxygen precipitates are incorporated into the oxide without a noticeable perturbation of oxide thickness. Thus, the oxide breakdown is attributed to oxygen precipitate induced shear stresses which decrease with increasing t{dollar}sb{lcub}rm ox{rcub}{dollar}. The nature of oxygen precipitates is totally different from that of D-defects; namely, it is an interstitial rather than vacancy related defect.; Individual D-defects transform to shallow surface etch pits during D-RAM processing which gives rise to local oxide thinning and rough surfaces, causing B-mode type gate oxide breakdown failures. The dissolution of D-defects by interstitial silicon injection, either dry oxidation at 1200{dollar}spcirc{dollar}C for 2hrs, or silicon ion implant with a dose of {dollar}1times10sp{lcub}13{rcub}{dollar} atoms/cm{dollar}sp2{dollar}, improves D-defect related gate oxide degradation. In addition, dry oxidation at 820{dollar}spcirc{dollar}C followed by wet oxidation at 950{dollar}spcirc{dollar}C reduces the extent of local oxide thinning caused by D-defects, which indicates that the D-defect induced oxide breakdown in a D-RAM device is associated with local oxide thinning and rough surfaces at the D-defect induced etch pit.; The above investigation clearly indicates that D-defects in CZ Si are cavities related vacancy condensation during crystal growth.