Influence of Humidity on Electrical Characteristics of Self-Assembled Porous Silica Low-k Films

Abstract

The influence of humidity on the dielectric constant and leakage current of self-assembled porous silica films which have two-dimensional hexagonal periodic porous structures was investigated quantitatively by proposing a new water adsorption model. The amount of H 2 O adsorption was calculated by the modified Rayleigh model, where H 2 O molecules are assumed to be adsorbed on the inner surface of cylindrical porous silica structures and form a dispersal concentric double-layer dielectric cylinder system. The amount of H 2 O calculated by the proposed model was consistent with the measured dielectric constant and thermogravimetry data. It suggests that inner-surface coverage of the cylindrical porous silica wall with a hydrophobic group is the most effective way to suppress water adsorption. Hexamethyldisilazane as a surface coverage molecule was introduced to the periodic cylindrical porous silica film and the leakage current was suppressed by a factor of 1/100 even below 0.5% relative humidity, resulting in the improvement of time-dependent dielectric breakdown lifetime by a factor of 30.Scaling of interconnects in ultralarge-scale integrated circuits ͑ULSI͒ has caused the increase of signal delay time due to the increase of interconnect resistance ͑R͒ and its parasitic capacitance ͑C͒, 1 while the transistor scaling is still effective to reduce the gate delay time. 2 For a 1-mm-long interconnect line fabricated on a Si chip, the RC delay time becomes a few hundred picoseconds, which is approximately 10 times larger than that of a metal oxide semiconductor field effect transistor ͑MOSFET͒. The RC delay time increases with decreasing the thickness and width of the metal interconnect as well as the spacing. In order to overcome this problem, copper and low-k interlayer dielectrics have been introduced. The interlayer dielectric films with the dielectric constants k ഛ 2.0 are required for future ULSI beyond 45 nm technology node. From the material point of view, various porous films have been developed to lower the dielectric constants. 3 However, the porous low-k films absorb moisture, resulting in the degradation of the film properties. To avoid this problem, a hexamethyldisilazane ͑HMDS͒ treatment has been commonly used to make the film hydrophobic.In this study, the influence of water adsorption on the dielectric constant and leakage current in the porous silica films 4 are investigated quantitatively, and the effect of HMDS treatment is discussed.Experimental p-Type Si substrates were cleaned in an RCA solution ͑NH 4 OH:H 2 O 2 :H 2 O = 36:720:1680͒ and dipped into a 0.5% HF solution. They were oxidized in O 2 ambient at 900°C to form 5 nm thick SiO 2 .A precursor solution for porous silica films was prepared by adding a surfactant, which was a PEO ͑polyethylene oxide͒-PPO ͑poly-propylene oxide͒-PEO triblock copolymer and an acidic silica sol derived from tetraethyl orthosilicate ͑TEOS͒ in ethanol diluted with water. The precursor solution was spin-coated on a Si substrate to form a homogeneous thin layer. Af...

Mechanism for difference in etched depth between isolated and dense via holes of SiOCH film

“…However, this estimation has several assumptions, especially in the reactions of additional H 2 O in the plasma and the move- 33 The models where the least amount of adsorbed water affects the dielectric constant of a low-k film were the modified Rayleigh model and the parallel model. 33 The former model assumes that water is adsorbed on the surface of pores in a low-k film, which agrees with the discussion of the TDS analysis. The latter model is a summation of each dielectric constant multiplied with volume fraction.…”

Ionic Conduction Leakage Current in Porous Silica Films

“…Here the dielectric constant was calculated from C-V measurement. By using modified Rayleigh model [1] and Kirkwood theory, we obtained number density of adsorbed water content (N H2O ) [2] as plotted in Fig.2. In this calculation we adopted arbitral constant values 0.01, 0.1, and 0.2 to volume ratio of water content for porous silica film (x), because we couldn't determine both x and dielectric constant of adsorbed water from only C-V measurement.…”

Electrical Breakdown in Advanced Interconnect Dielectrics

“…Too high a testing temperature cannot be used [265,266], unless one is testing to directly assess the impact of such free Cu. Moisture ingress in LK/ULK dielectrics is known to have a deleterious effect on low-k leakage [273][274][275], dielectric breakdown strength, and field acceleration [276][277][278][279][280][281][282] and may be made worse when interfaces are present that lie along the electric field lines, as is the case for IMD capacitors [234]. The low activation energy of oxide breakdown also justifies the notion stated above about testing at a moderately high temperature for intrinsic (or integrated intrinsic) reliability assessment.…”