Electric field and temperature-induced removal of moisture in nanoporous organosilicate films

Abstract

The effects of bias-temperature-stress ͑BTS͒ or simply temperature-stress ͑TS͒ on nanoporous low-k methylsilsesquioxane films are studied. Initially, the as-given and O 2 ashed/etched films exhibit physical adsorption of moisture as revealed from the electrical behavior of the samples after 15 days. The temperature stressing at 170°C volatilized the adsorbed water but is unable to remove chemisorb and hydrophillic Si-OH groups. As a result, the TS films remain susceptible to moisture. BTS at 170°C also removes adsorbed water. More important, the surfaces under the metal-insulator structure were dehydroxylated by breaking the chemisorb Si-OH group facilitating the formation of siloxane bonds that prevents adsorption of moisture even after 60 days. © 2004 American Institute of Physics. ͓DOI: 10.1063/1.1757019͔As device dimensions shrink, the struggle to find ultralow dielectric constant ͑k͒ materials for future generation integrated circuits ͑ICs͒ continues unabated. Although many low-k materials in the range of 2.0-4.0 1-5 have been studied, integration problems and issues like moisture adsorption brought numerous reliability concerns. Methylsilsesquixane ͑MSQ͒ is an attractive candidate for replacement of SiO 2 in future generation ICs because of its inherent low-k ͑2.8͒ and good thermal stability. The introduction of nanopores to MSQ provides extendibility of dielectric constant to values lower than 2.0. However, the dielectric properties of this nanoporous material are seriously degraded during photoresist removal-an important microelectronic fabrication step that involves O 2 ashing/etching. 6,7 This process also removes the hydrophobic CH x groups from exposed surfaces ͑pore surface as well͒ of the film and allowing the formation of silanol ͑Si-OH͒ groups. As a result, the hydrophillic Si-OH enhances physical adsorption of moisture upon air exposure and increases the dielectric constant. This causes device reliability problems. Device instabilities could occur causing an increase in leakage currents that may lead to breakdown of the dielectric film.Current work focuses on studying the effects of biastemperature-stress ͑BTS͒ or temperature-stress ͑TS͒ of nanoporous MSQ. BTS has been a very effective method to detect device instabilities like the presence of mobile ions or diffusion of metal ions in the dielectric. The time-dependent moisture adsorption and thermal stability of as-given and O 2 ashed/etched MSQ films are also investigated. This study will attempt to explain the susceptibility of MSQ films to moisture after BTS or TS.The nanoporous MSQ films studied are courtesy of Tokyo Electron America ͑TEL͒. The as-given and O 2 ashed/ etched MSQ for electrical measurements have thicknesses of 390 and 280 nm, respectively. To fabricate metalinsulator-semiconductor ͑MIS͒ devices, metal dots of titanium with an area 4.9ϫ10 Ϫ4 cm 2 were sputter-deposited. The capacitance-voltage (C -V) measurements were carried out on HP4284 LCR meter while current-voltage measurements were carried out on Keithly 2400 Sourcemet...

High performance In2O3 thin film transistors using chemically derived aluminum oxide dielectric

“…The high value of capacitance in case of the low temperature annealed AlO x films may attribute to the presence of OH-groups. 22 The schematic of the TFT structure used in this work is shown in Fig. 3(a).…”

Field-Effect Mobility Extraction of Solution-Processed InGaZnO Thin-Film Transistors Considering Dielectric Dispersion Behavior of AlOx Gate Insulator

“…The dielectric dispersion of solution-processed AlO x film was attributed to the existence of mobile ions and residues from the incomplete chemical reaction. 11,21 The mobile ions, such as hydrogen ion (H + ) and hydroxyl group (OH − ), form an electric double layer (EDL) in the AlO x layer when the electric field is applied across the layer. 8,9,11 Figure 3 shows the TOF-SIMS result of the AlO x layers annealed at 350 and 500 °C in the MIM capacitor.…”

“…The AlO x dielectric film annealed at 350 °C exhibited frequency-dependent capacitance, that is, dielectric dispersion behavior, while the AlO x film annealed at 500 °C showed constant capacitance values over a range between 20 Hz and 100 kHz. The dielectric dispersion of solution-processed AlO x film was attributed to the existence of mobile ions and residues from the incomplete chemical reaction. , The mobile ions, such as hydrogen ion (H + ) and hydroxyl group (OH – ), form an electric double layer (EDL) in the AlO x layer when the electric field is applied across the layer. ,, Figure shows the TOF-SIMS result of the AlO x layers annealed at 350 and 500 °C in the MIM capacitor. Although other residual impurities, such as chloride ion (Cl – ), can also affect the dispersive behavior, we focused on H + and OH – ions because the AlO x films contained substantially more H + and OH – ions than other residual impurities (Figure S5).…”

Electrical Breakdown in Advanced Interconnect Dielectrics

“…Dielectric breakdown is generally expected to have low activation energy (E a ≤ 0.5 eV) [221,[267][268][269] as opposed to Cu drift-diffusion controlled breakdown (E a ≥ 1.0 eV) [259] so that their individual contributions to dielectric breakdown can be determined (rather painfully) by testing over a wide temperature range [270]. Volatizing adsorbed moisture with heat treatment [283] certainly helps (especially if done during chip fabrication), but chemisorbed and hydrophilic species are not removed by heat treatment and can reabsorb moisture during subsequent processing [284]. Only modest benefit in testing efficiency is found by testing at much higher temperatures for a failure mechanism with intrinsically low activation energy.…”