Nitrogen incorporation in ultrathin gate dielectrics: A comparison of He/N2O and He/N2 remote plasma processes

Khandelwal, Amit; Smith, Bradley C.; Lamb, H. Henry

doi:10.1063/1.1397286

Cited by 15 publications

(7 citation statements)

References 42 publications

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“…For ultrathin SiO 2 films ͑Ͻ1 nm͒ processed at 0.3 Torr, previous experiments have shown that nitrogen diffuses through the superficial oxide, and bonds at the Si-SiO 2 interface. 21,22 These observations suggest that the nitridation mechanism changes from ''nondiffusive'' ͑charged particle-assisted͒ to ''diffusive'' ͑presumably involving neutral N species͒ as the process pressure is increased from 0.1 to 0.3 Torr. The very low nitridation rate measured at 0.1 Torr using a N 2 remote plasma indicates that He dilution provides a strong nitridation rate enhancement.…”

Section: Discussionmentioning

confidence: 95%

Reaction pathways in remote plasma nitridation of ultrathin SiO2 films

Niimi

Khandelwal

Lamb

et al. 2002

Journal of Applied Physics

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Low-temperature nitridation of 3 nm SiO2 films using He/N2 and N2 remote radio frequency (rf) plasmas was investigated. On-line Auger electron spectroscopy and angle-resolved x-ray photoelectron spectroscopy (ARXPS) were employed to determine the concentration, spatial distribution, and local chemical bonding of nitrogen in the resultant films. Experiments were performed using a substrate temperature of 300 °C and 30 W rf power. Nitridation using an upstream He/N2 remote plasma at 0.1 Torr incorporates nitrogen at the top surface of the SiO2 film. In contrast, a lower concentration of nitrogen distributed throughout the film is obtained when the process pressure is increased to 0.3 Torr. ARXPS indicates a N–Si3 local bonding configuration, irrespective of the spatial distribution of N atoms. Slightly more nitrogen is incorporated using a downstream He/N2 plasma at each process pressure. By comparison, nitridation of SiO2 films using a N2 remote plasma at 0.1 Torr is very slow. Optical emission spectroscopy indicates that He dilution enhances the generation of N2+(B 2Σu+) species by altering the plasma electron energy distribution and by providing an additional kinetic pathway (Penning ionization). Changing the He/N2 remote plasma configuration from upstream to downstream (at 0.1 and 0.3 Torr) also enhances N2+(B 2Σu+) generation. For upstream He/N2 remote plasmas, the intensity of N2 first positive emission from N2(B 3Πg) states increases with pressure, whereas the N2+ first negative emission from N2+(B 2Σu+) states decreases. We infer from these observations that N2+ species are primarily responsible for top surface nitridation at 0.1 Torr, and that neutral species [N2(A 3Σu+) metastables and N atoms] are associated with sub-surface nitrogen incorporation.

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Section: Discussionmentioning

confidence: 95%

Reaction pathways in remote plasma nitridation of ultrathin SiO2 films

Niimi

Khandelwal

Lamb

et al. 2002

Journal of Applied Physics

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“…19 The higher concentration of reactive oxygen species thus results in more extensive replacement of nitrogen atoms in the bulk, and especially in the interfacial region of nitrided hafnium oxide films with the silicon substrate. 26,27 Higher concentration of reactive oxygen species also results in more completely oxidized hafnium ions in the interfacial regions of films deposited in nitrous oxide. For the above reasons, lower nitrogen concentrations exist at the interface of nitrous oxide-deposited films with silicon relative to those of films deposited in oxygen.…”

Section: F2mentioning

confidence: 99%

Comparison of Nitrided HfO[sub 2] Films Deposited in O[sub 2] and N[sub 2]O by Direct Liquid Injection CVD

Luo¹,

Dragomir-Cernatescu

Snyder

et al. 2006

J. Electrochem. Soc.

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Nitrided HfO 2 films are deposited by direct liquid injection chemical vapor deposition ͑CVD͒ using O 2 or N 2 O as oxidants. Deposition kinetics, phase, chemical composition, bonding, and dielectric properties of the films obtained from the two different oxidants are compared. Depositions in nitrous oxide display an activation energy ͑9.9 kcal/mol͒ less than that observed with oxygen ͑13.6 kcal͒. Films obtained from nitrous oxide are amorphous as determined by grazing incidence X-ray diffraction, while films deposited using oxygen are mixtures of amorphous and crystalline phases. Films deposited from nitrous oxide have lower bulk and interface ͑with silicon͒ nitrogen concentrations relative to films deposited in oxygen. The amorphous structure of nitrous oxide deposited films and an enhanced concentration of oxygen atoms from nitrous oxide are believed to be the reasons for the reduced interface nitrogen concentrations. Capacitance-voltage measurements demonstrate that films deposited with nitrous oxide have lower dielectric constants and lower interface trap densities relative to films deposited from oxygen. Leakage currents of the films deposited in nitrous oxide are smaller than those of films deposited in oxygen. Nitrogen concentration and oxygen content at the film/silicon substrate interface appear to be the reason for the distinct electrical properties of films deposited using the two oxidants.As the minimum feature size in complementary metal-oxidesemiconductor ͑CMOS͒ devices approaches 60 nm, 1 the gate dielectric thickness will fall below 1.5 nm. For the current gate material SiO 2 , the leakage current of a film Ͻ1.5 nm will increase sufficiently to impair device operation. Thus, high-dielectric-constant ͑high-k͒ materials are being investigated as replacements for SiO 2 in CMOS devices in order to reduce this leakage. Because the dielectric constants of high-k materials ͑usually Ͼ 10͒ are larger than that of SiO 2 ͑ = 3.9͒, the high-k gate layer can be physically thicker than a capacitively equivalent SiO 2 gate layer ͑t high-k / high-k = t SiO 2 / SiO 2 ͒; as a result, the leakage current is reduced. Recently, a number of binary and ternary metal oxides have been studied as candidates for new gate dielectrics, including Al 2 O 3 , 2 ZrO 2 , 3 HfO 2 , 4-6 and ͑Zr, Sn, Ti͒O 2 . 7,8 Because of its high dielectric constant ͑15-25͒, large bandgap ͑5.68 eV͒, and thermal stability with silicon, attention has focused on HfO 2 -based high-k materials. 4-6 In order to improve the thermal stability and resistance to oxygen and dopant diffusion, nitrogen atoms are sometimes introduced into HfO 2 films. Nitrided HfO 2 films have been obtained by ammonia annealing of deposited HfO 2 films 9 by the use of amide precursors ͑e.g., Hf͓N͑CH 3 ͒ 2 ͔ 4 and Hf͓N͑C 2 H 5 ͒ 2 ͔ 4 ͒, 10-14 or by incorporation of nitrogen-containing reactants such as NH 3 into chemical vapor deposition ͑CVD͒ processes. 15 In order to optimize the electrical properties of HfO 2 -based dielectrics, variations in the CVD process have been studi...

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“…N 2 O is completely dissociated in the plasma at these power densities, and the signal at m / z (mass-tocharge ratio͒ = 44 is due to CO 2 + formed from the reaction of atomic oxygen with residual carbon on the walls of the reactor chamber. Some peaks in the region between 300 and 500 nm may be caused by the first negative system of the 19 Each spectra also shows a small peak at 821 nm that is attributed to atomic N. 20 No emission from NO was detected in this system. 1 were only weakly impacted by power over the range studied.…”

Section: A Icp Source Characterizationmentioning

confidence: 83%

A comparison of plasma-activated N2∕O2 and N2O∕O2 mixtures for use in ZnO:N synthesis by chemical vapor deposition

Barnes

Leaf

Hand

et al. 2004

Journal of Applied Physics

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Electrical and optical studies of metal organic chemical vapor deposition grown N-doped ZnO films ZnO synthesis by high vacuum plasma-assisted chemical vapor deposition using dimethylzinc and atomic oxygen J.A high-vacuum plasma-assisted chemical-vapor deposition system was used to systematically study ZnO:N thin film synthesis. Nitrogen doping was achieved by mixing either N 2 O or N 2 with O 2 in a high-density inductively coupled plasma (ICP) source. In situ diagnostics showed that the ICP composition was predominantly a function of the elemental oxygen to nitrogen ratio, and relatively insensitive to the choice of N 2 or N 2 O as the molecular precursor. Nitrogen incorporation was measured by both x-ray photoelectron spectroscopy and secondary ion mass spectrometry and was found to increase monotonically with both N 2 O and N 2 addition. Nitrogen doping was correlated with systematic shifts in the lattice spacing, electrical conductivity, and optical absorption. Quantitative comparisons between film properties and gas composition suggest that atomic nitrogen is the primary precursor for doping in this system.

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Nitrogen incorporation in ultrathin gate dielectrics: A comparison of He/N2O and He/N2 remote plasma processes

Cited by 15 publications

References 42 publications

Reaction pathways in remote plasma nitridation of ultrathin SiO2 films

Reaction pathways in remote plasma nitridation of ultrathin SiO2 films

Comparison of Nitrided HfO[sub 2] Films Deposited in O[sub 2] and N[sub 2]O by Direct Liquid Injection CVD

A comparison of plasma-activated N2∕O2 and N2O∕O2 mixtures for use in ZnO:N synthesis by chemical vapor deposition

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