An Investigation of Fixed Charge Buildup in Nitrided Oxides

Thermally grown silicon dioxide thin films on silicon were nitrided in 1 atm NH3 at 1150°C for various times between 10 and 240 min. The films were between 12 and 163 nm thick. Chemical kinetics severely limited the incorporation of nitrogen into the film; only the thinnest films nitrided for times longer than 90 min attained a nitrogen content near 40 atomic percent nitrogen. Secondary ion mass spectrometry indicated that nitridation either lowered or maintained the average hydrogen concentration in the film. Infrared spectroscopy demonstrated that nitridation removed silanol groups from a film which had been grown in wet oxygen. In certain films, over 99% of the nitrogen in the film was incorporated into the tetrahedral network; less than 1% of all nitrogen in the film existed as silamine groups. Nitridation increased (i) the 1 MHz dielectric constant and (ii) the electron‐trapping ability of a film; these two properties were correlated to replacement of nitrogen for oxygen in the film bulk. Creation of a nitrogen‐rich layer at the Si/film interface after 10 min of nitridation was correlated to an increase in fixed insulator charge density, Nnormalf . At nitridation times of 30 min and longer, the silicon substrate was reoxidized by water released by the nitridation of the film near the interface. Reoxidation of the silicon steadily lowered Nnormalf .

Section: Electrical Resultssupporting

confidence: 92%

Thermal Nitridation of SiO2 Thin Films on Si at 1150°C

Koba

Tressler

1988

“…Previous research focused on the electrical properties of nitrided oxides not subjected to any postnitridation thermal treatments (anneals). These previous studies indicated that oxides nitrided at 950~ exhibited higher Nf and D~t than similar films nitrided at 1050 ~ and 1150~ (9,10). For this reason, a nitridation temperature of 950~ was selected for this investigation.…”

mentioning

confidence: 99%

“…treatment was known to reduce Dit substantially (9), and the 950~ nitridation to increase Nf significantly (7,10,(12)(13)(14). The differences in results strongly suggested that the two treatments were largely dissimilar; by employing IR spectroscopy, it was hoped that some insight into the nature of the differences could be obtained.…”

mentioning

confidence: 99%

Properties of SiO2 on Si after Exposure to 3:1 H 2 + N 2 and NH 3

Ruggles

Koba

Tressler

1986

Thermal oxides ≃100 nm thick were exposed to 3:1 H2+N2 for 30 min at 950°C; similar films were treated in pure ammonia for 30 min at 950°C. The oxides were examined by high frequency and quasi‐static capacitance‐voltage measurements. A silicon internal reflection element (IRE) was processed in a similar manner in order to assess the effects of the thermal processing on the infrared spectrum of the thin film. The IRE was used for attenuated total reflection infrared spectroscopy, a technique that provides greater sensitivity to molecular groups such as Si‐OH, normalSi‐NHx , Si‐H, H2O , and NH3 (1, 2). Secondary ion mass spectrometry revealed the quantitative distributions of N, O, and H throughout a sample film. Ammonia exposure resulted in replacement of oxygen by nitrogen in the amorphous tetrahedral network. Films annealed in 75%H2:25%N2 (the expected dissociation products of NH3 ) were found to exhibit significantly different properties from films nitrided in NH3 , because NH3 did not attain thermodynamic equilibrium before coming in contact with the films. The H2+N2 anneal apparently increased the degree of oxygen bridging in SiO2 . Based on the IR data, a new model is proposed to explain the annealing of interface traps via H2 . Hydrogen is suspected to act as a catalyst, promoting bond rearrangement in the amorphous network. Nonbridging oxygen atoms are thought to bond to dangling silicon orbitals at the oxide/Si interface, thereby reducing the density of defects responsible for Dnormalit .

“…The reason that devices with dielectrics grown in N~O ambient show smaller Nf may be due to the fact that these dielectrics contain much smaller concentration of H or H-related species, as indicated by SIMS results (not shown). In NH~-nitrided SiO~, H~-induced Si--O bond breaking and bond dissociation via NH~ (x = 1,2) result in the formation of trivalent silicon defects and the nonbridging oxygen atoms, both of which could behave as fixed positive charge (14). The other explanation for the fixed charge buildup is the incorporation of nitrogen at the Si/SiO~ interface, similar to what has 4) that the fixed charge buildup in NHa-nitrided oxides is determined by a defect generation process associated with nitrogen incorporation and an annealing-type process which is more effective at high temperature.…”

Section: Resultsmentioning

confidence: 99%

High Quality Ultrathin Gate Dielectrics Formation by Thermal Oxidation of Si in N 2 O

Ahn

Ting

Chu

et al. 1991

maintained by charge-discharge cycling. The a-V2Os-P205 had no diffraction patterns except due to PTFE and graphite.The IR spectra at various stages of c-V2Os and e-V2Os cycling are shown in Fig. 6. The IR spectra of a-V2Os-P2Os gave unclear absorption spectra due to V=O and V--O bonds and almost did not change upon discharge and charge cycling. In the case of c-V2Os [Fig. 6(a)~] the absorption due to V--O stretching disappeared when it was discharged to 2.0 V(B) and the absorption due to V--O double bond also disappeared when it was discharged to 1.0 V(D) (12). This did not reverse even after charging to 3.5 V(E). On the contrary, e-V20~ [Fig. 6(b)] kept its structure even after discharging to 1.0 V(D) and then charging to 3.5 V(E). This shows e-V2Os is more resistant to the structure expansion due to lithium intercalation-deintercalation than c-V205. As the structural change for e-V205 did not occur by Li intercalation-deintercalation, the next charging after discharging is possible without capacity loss, i.e., the structure for Li insertion is maintained. Longer cycle life for deep discharge depth may be possible. These x-ray and IR data explain the less disruption of the structure for e-V205 and a-V2Os-P205 compared to c-V205.