Porous Dielectrics Research Articles

Surface-Localized Sealing of Porous Ultralow-k Dielectric Films with Ultrathin (

Semiconductor integrated circuit chip industries have been striving to introduce porous ultralow-k (ULK) dielectrics into the multilevel interconnection process in order to improve their chip operation speed by reducing capacitance along the signal path. To date, however, highly porous ULK dielectrics (porosity >40%, dielectric constant (k) <2.4) have not been successfully adopted in real devices because the porous nature causes many serious problems, including noncontinuous barrier deposition, penetration of the barrier metal, and reliability issues. Here, a method that allows porous ULK dielectrics to be successfully used with a multilevel interconnection scheme is presented. The surface of the porous ULK dielectric film (k = 2.0, porosity ∼47%) could be completely sealed by a thin (<2 nm) polymer deposited by a multistep initiated chemical vapor deposition (iCVD) process. Using the iCVD process, a thin pore-sealing layer was localized only to the surface of the porous ULK dielectric film, which could minimize the increase of k; the final effective k was less than 2.2, and the penetration of metal barrier precursors into the dielectric film was completely blocked. The pore-sealed ULK dielectric film also exhibited excellent long-term reliability comparable to a dense low-k dielectric film.

Modeling and Simulation of Cu Diffusion in Porous Low-k Dielectrics

A modeling and simulation study of metal atom diffusion in porous dielectrics is presented using elementary jump frequencies for a random walk in 2D and 3D. The simulation is calibrated with experimental data from Cu/porous SiCOH/W structures. The effective Cu diffusivity is shown to depend not only on the level of porosity but also on the pore morphology. Other important factors: i) surface diffusion on the inner pore surfaces vs diffusivity in the bulk matrix material, ii) the rate of Cu dissolution into the dielectric vs the rate of transport by diffusion, and iii) the degree of the contact area of the Cu electrode with the porous dielectric surface, are also taken into account. The large multitude of porosity effects on diffusivity can be consistently and intelligibly explained in terms of “channeling” and “trapping” effects based on perturbation of local vertical and lateral concentration gradients imparted by the pore morphology.

Modeling and Simulation of Cu Diffusion in Porous Low-k Dielectrics

Integrating nanometer sized pores into low-k ILD films is one of the approaches to lower the RC signal delay and thus help sustain the continued scaling of micro-electronic devices. While increasing porosity of porous dielectrics achieves the desirable lowering of the dielectric constant (k), it also creates a myriad of reliability and implementation issues. One of the problems is the little understood metal diffusion in porous media. Here, we present a rigorous simulation method of Cu diffusion based on master equation with elementary jump probabilities within the contiguous dielectric film, along the pore boundary, from the dielectric matrix to the pore boundary, and from the pore boundary to the matrix material. In view of the diffusional jump distance being as large as 2 nm, the nano-pores being on a similar length scale, and the film thickness being only a few tens of nanometers, the conventional diffusion equation in differential equation form is grossly inadequate and elementary jump frequencies are required for a proper description of the Cu diffusion in porous dielectric. The present atomistic approach allows a consistent implementation of Cu ion drift in electric field by lowering and raising of the diffusion barriers along the field direction. Two numerical methods are being used to evaluate the atomistic Cu transport: 1) Diffusion tensor theory (4th rank tensor in 2D, 9th rank in 3D), 2) Sequential lattice point evaluation of elementary diffusion jumps. The 2nd method is very efficient in 3D, where the simulation time increases only linearly with the dimension of the matrix, while the 1st method allows an easy implementation of jump frequencies at the boundaries of the film and pore boundaries.

Accurate Measurement of Porous Low-k Thin-Films by Nanoindentation: Densification Scaling versus Substrate Effects

Historically, the integration of insulators with decreasing dielectric constants, k, has been critical in improving devices performance. The most efficient approach to decrease k is by introducing porosity. Since porosity directly impacts the Young's modulus, the accurate determination of the mechanical properties of porous dielectrics is essential in enabling their implementation into state-of-the-art devices. Currently, nanoindentation is the technique of choice, but as technology relevant thicknesses of dielectrics keep decreasing, substrate effects are unavoidably encountered. These issues have so far been circumvented by measuring bulk materials instead of their thin-film counterparts. This approach is, however, less than ideal as physical properties can be size-dependent. Moreover, pores densification also occurs, potentially leading to overestimated Young's modulus values. In this paper, we define a novel protocol based on ultra-low load, quasi-static nanoindentation to measure mechanical properties of porous thin-films as a function of porosity (0–60%) and thickness (150–700 nm). We could isolate materials densification from substrate effect, and we demonstrated that the former can be accounted for, while the latter does not happen until indentation depths are remarkably higher than the traditionally accepted indentation limit of 10% of the film thickness. Consequently, extremely accurate mechanical characterization of porous low-k thin-films is now possible.

Dielectric loss in porous TiO2

The dielectric loss behavior of TiO2 was characterized on samples of variable porosity and variable pore size. Pores were formed by two methods: varying the sintering temperature and by the addition of a spherical carbon porogen. Porosities varied from 5.9% to 59.3%. Dielectric loss increased with increasing pore volume in each case. However, dielectric loss increased at a slower rate for porogen induced pores. At equivalent pore volumes, pore surface area volumes were higher than those induced using the porogen. Dielectric loss behavior was shown to vary linearly with pore surface area. Our work demonstrates that large pores reduce free surface area and decrease dielectric loss when compared to similar samples with smaller pores. A new model of porous dielectric loss is proposed that characterizes materials based on generalized free surface area instead of porosity alone. Based on this model, we show that the relative loss of porous dielectrics depends critically on the pore surface area and the loss tangent of the parent dielectric.

Characterization of Porous BEOL Dielectrics for Resistive Switching

Porous back-end dielectric materials with porosity ranging from 8% to 25% have been characterized in terms of their resistive switching behavior. The porous dielectric is sandwiched between Cu and W or Pt electrodes. Some metal-insulator-metal structures have a 2 nm SiCN diffusion barrier at either electrode or at both electrodes. 90% of samples are intrinsically conductive due to strong Cu doping of the dielectric. About 10% of the samples display resistive switching behavior, of which devices with two SiCN barriers can be switched repeatedly, demonstrating that resistive switching in porous dielectrics is feasible. The forming voltage of the filaments increases with increasing porosity of the dielectric. Depending on the voltage polarity, Cu and oxygen vacancy conductive filaments can be formed. The properties of resistive switching established in this work provide a solid basis for further improvement of ReRAM devices based on porous dielectrics compatible with CMOS backend.

Decoupling of Ion Diffusivity and Electromobility in Porous Dielectrics

Porous back-end dielectric materials with porosity from 8% to 25%, sandwiched between Cu and W/Pt electrodes, have been investigated in terms of Cu diffusivity and mobility. In nonporous materials the diffusivity D and mobility m of charged particles such as an ion is related by the Einstein relation: μ=D q/kT. Here, we present evidence that in porous materials the diffusivity and mobility are decoupled on a global scale, even though the Einstein relation still holds locally. In porous materials, the voids lying in the path of the ion present an impenetrable barrier for ion migration. Voids can be only overcome by a detour around the obstacle by virtue of diffusion. We propose a modified relation between diffusivity and mobility in porous materials by μ=fp∙D q/kT where a porosity-tortuosity factor fp <1 is introduced. The factor fp depends on porosity and tortuosity of the porous material.

Characterization of Porous BEOL Dielectrics for Resistive Switching

Building nonvolatile memory directly into a CMOS low-k/Cu interconnects would reduce latency in connectivity constrained computational devices and reduce chip’s footprint by stacking memory on top of logic. In the relentless drive to lower the interconnect time delay, porous low-k dielectrics are being currently explored. In this paper, porous dielectrics are being electrically characterized and their suitability for resistive switching (RS) assessed. Metal-Insulator-Metal (MIM) structures have been manufactured with bottom Cu electrode and with top island-shaped W or Pt counter-electrode. The porous dielectric was a-SiC:H or a-SiOC:H with level of porosity varying between 8% to 25%. The thickness of the porous dielectric is 20 nm and the dielectric constant k varied between 3.1 (@ 8% porosity) and 2.5 (@25% porosity). Some devices have a 2 nm SiCN diffusion barrier (DB), either at the Cu or W/Pt electrode or at both electrodes. The SiCN layers serve a dual-purpose: i) to prevent Cu diffusion, and ii) to prevent Cu, W, and Pt protrusion into pores and voids of porous dielectrics. A bulk majority of devices has been found conductive from the beginning and less than 10% - only those with at least one DB - displayed RS behavior. The intrinsic conductive state has been found to scale with the area of the top island electrode, and its temperature coefficient of resistance (TCR) has been found to be TCR=0.0028 K-1. Both findings are consistent with high concentration of Cu in the dielectric indicating bulk conduction. This means that porous dielectrics are vulnerable to metal diffusion and even two diffusion barriers of 2 nm are marginal in arresting Cu diffusion. When subjected to resistive switching, the intrinsic resistance Rint was found to be dependent on the applied compliance current Icc. Rint decreases linearly with increasing Icc when Icc is smaller than a critical value Icc(crit), typically 10 mA; for Icc larger than Icc(crit) Rint is constant. This finding is explained with improved ionization of copper and more homogenous Cu distribution through out the dielectric. The RS behavior was tested in two modes: a) positive bias applied, and b) negative bias applied to Cu electrode, while W/Pt electrode are being grounded. At positive bias, a few samples displayed resistive behavior where a Cu filament could be formed, and subsequently reset and set several times. Thus, as a proof of concept, it has been demonstrated that resistive switching can be realized in porous dielectrics. It has been found that devices with W electrode showed superior behavior compared to Pt devices. Best resistive switching behavior was found with dielectric of 25% and with both SiCN barriers at Cu and at W electrode. The filament formation at positive and negative bias results in different type of a filament. Filaments formed at positive bias applied to Cu electrode are Cu filaments and filaments formed at negative bias are attributed to defects or broken bonds of the dielectric matrix. Measurements of temperature coefficient of resistance (TCR) have confirmed that both types of filaments have substantially different TCR coefficients. TCR of the filaments created at positive and negative bias has been measured and found to be 0.0031 K-1 for positive and 0.0021 K-1 for the negative bias, respectively. TCR=-0.0031K-1 has been found to be characteristic of Cu filaments in Cu/TaOx/Pt devices, and TCR=0.0021K-1 is consistent with oxygen vacancy filaments in the same devices. Hence, filaments with 0.0031K-1 have been identified with Cu filaments and filaments with 0.0021K-1 with defect filaments. Those devices that have shown resistive switching were found to be sensitive to the level of Icc. For Icc<100 mA the on-state is volatile, i.e. the device reverts to the off-state when it is no longer powered. For Icc>1 mA, the on-state was non-volatile. In many cases, the non-volatile state was a permanent one, i.e. the device could not be reset. Devices that were not conductive from the beginning were subjected to a 5 min anneal at 40 oC, 60 oC, and 100 oC. The electrical measurements confirm that with increasing temperature more and more samples became intrinsically conductive; at 100 oC all the samples (including those with two diffusion barriers) became intrinsically conductive. These results confirm that the devices suffer from excessive Cu diffusion at the manufacturing stage of the devices. Surprisingly, it has been also found that – for those devices that displayed resistive switching – the forming voltage increased with increasing level of porosity. The present study gives good insights and establishes a solid data base for further improvement of the implementation of porous dielectrics into CMOS BEOL.

Decoupling of Ion Diffusivity and Electromobility in Porous Dielectrics

In an effort to lower the interconnect time delay and address the latency problem, porous low-k dielectrics are being currently explored as a low-k BEOL dielectric. Because of low density, porous dielectrics suffer from excessive impurity diffusion and from ion electromigration when the interconnect lines are powered. This paper investigates the relation of ion diffusivity and electro-mobility in porous dielectrics. Metal-Insulator-Metal (MIM) structures have been manufactured with bottom Cu electrode and with top island-shaped W or Pt counter-electrode. The porous dielectric was a-SiC:H or a-SiOC:H with level of porosity varying between 8% to 25%. The thickness of the porous dielectric is 20 nm and the dielectric constant k varied between 3.1 (@ 8% porosity) and 2.5 (@25% porosity). Some devices have a 2 nm SiCN diffusion barrier (DB), either at the Cu or W/Pt electrode or at both electrodes. The SiCN layers serve a dual-purpose: i) to prevent Cu diffusion, and ii) to prevent Cu, W, and Pt protrusion into pores and cavities of porous dielectrics. A bulk majority of devices have been found intrinsically conductive, i.e. conductive from the beginning and less than 10% - only those with at least one DB - displayed resistive switching (RS) behavior. Of those devices that showed resistive switching behavior, devices with higher porosity showed consistently higher forming voltage Vform of Cu filaments than dielectrics with lower porosity. This is strange in view of the fact that most of the devices even of high porosity where intrinsically conductive indicating a very high degree of Cu diffusion. For a-SiC:H film with 8% porosity we find Vform ≈ 0V, compared with Vform= 0.4 - 0.5V for 12% porosity and Vform= 1.4 V- 2.3 V for 25% porosity. Why should electromigration require higher electric field when the Cu diffusivity appears to be equally strong? In nonporous materials the diffusivity D and mobility m of charged particles such as an ion is related by the Einstein relation:, where k is the Boltzmann constant, T the absolute temperature and q the charge of the ion. In terms of microscopic mechanisms, diffusivity and mobility are very related phenomena. The difference between diffusion and mobility is that the applied electric field lowers the barrier for the forward jump and increases the barrier for the reverse jump in the direction of the electric field. In two and three dimensions the difference between diffusion and electromigration is that diffusion is isotropic in homogeneous materials and electromigration is directional. We postulate that in porous materials the diffusivity and mobility are decoupled and the Einstein relation does not hold globally but only locally within a contiguous patch of material outside of the voids constituting the porosity. In porous materials, the voids lying in the path of the migrating ion present an impenetrable barrier for electromigration. They can be only overcome by a detour around the obstacle that can be brought about only by the driving force of diffusion. Thus an ion encountering a void in its path has to rely on diffusion to circumnavigate the obstacle. We propose that the relation between diffusivity and mobility in porous materials should be described by a revised relation: where a porosity factor fp <1 is introduced. The factor fp will depend on porosity, such that fp = f(porosity) will decrease with increasing porosity. The revised relation between diffusivity and mobility has to be understood as a macroscopic relation. Within the dense matrix of the material between the voids, the classic Einstein relation will still hold microscopically. But, in porous materials the obstacles posed by the voids compromise the directional nature of the mobility. We propose a numerical model where the porosity factor fp of the revised Einstein relation can be modeled as a function of porosity in two dimensions. An extension to three dimensions is also feasible, but requires larger computational resources.

Low Dielectric Constant, Air-Cavities Created By the Use of Low-Ceiling Temperature Polymers

Low decomposition temperature (<200oC) template polymers that decompose into gaseous products have been used as templating materials in the formation of air-cavities and porous dielectrics. It is especially important for the sacrificial, templating polymer to decompose cleanly to gaseous products at a specific temperature, which is compatible with the other materials present, especially the dielectric superstructure surrounding the sacrificial material. It is also important for the sacrificial polymer to leave little or no residue so that undesirable materials are not formed during the process. One method of producing a low-temperature sacrificial material is the use of a low ceiling temperature polymer. Above the ceiling temperature, the polymer reverts back to monomers. A polymer with a low ceiling temperature can rapidly depolymerization back to monomer and vaporize, if the monomer vapor pressure is suitably high at room temperature (>10 Torr). This work focuses on the synthesis and decomposition of low ceiling temperature polyaldehydes using high vapor pressure monomers. Polyphthalaldehyde could be used as the template polymer for creating air-gaps and porous dielectrics. Polyphthalaldehyde has a moderate decomposition temperature of 125oC and a moderate vapor pressure. Copolymers of aldehydes are of interest because the vapor pressure of the sacrificial polymer decomposition products can be increased. Polyaldehyde copolymers were synthesized with the goal of increasing the thermal decomposition temperature and increase the evaporation rate of the decomposition products. A random copolymer of phthalaldehyde and butyraldehyde raised the 50 percent decomposition temperature of the polyaldehyde by 25oC when compared to the phthalaldehyde. homopolymer. Even a small amount of the higher vapor pressure monomer, butyraldehyde, increased the evaporation rate substantially.

Characterization of Patterned Porous Low-k Dielectrics: Surface Sealing and Residue Removal by Wet Processing/Cleaning

The results described in this paper first demonstrate key differences between a plasma-exposed blanket porous dielectric sample and a patterned structure in terms of surface sealing induced by the patterning plasma using ellipsometric porosimetry characterization. While the blanket CVD organosilicate glass (nominal k-value = 2.4, ∼20% of porosity) surface was sealed by the C4F8/CF4-based plasma, the surface of the analogous patterned structure of 45 nm 1/2 pitch was found to be completely open after the same patterning plasma process. Second, the surface composition of the patterned feature, type of the residues generated during the plasma etch, and the effect of a subsequent wet clean step are presented. The experimental results demonstrate that the use of a relevant patterned test structure and its characterization represent an appropriate approach for the optimization of the etch and cleaning processes. The removal efficiency of various wet clean solutions, including dilute HF, citric acid, tetramethylammonium hydroxide:H2O2:H2O mixture, and a slightly alkaline formulated mixture, with regard to polymer residues, CFx, and metal-containing residues, TiFx, can be clearly distinguished using the patterned porous low-k stack.

Vacuum ultra-violet damage and damage mitigation for plasma processing of highly porous organosilicate glass dielectrics

Porous organosilicate glass thin films, with k-value 2.0, were exposed to 147 nm vacuum ultra-violet (VUV) photons emitted in a Xenon capacitive coupled plasma discharge. Strong methyl bond depletion was observed, concomitant with a significant increase of the bulk dielectric constant. This indicates that, besides reactive radical diffusion, photons emitted during plasma processing do impede dielectric properties and therefore need to be tackled appropriately during patterning and integration. The detrimental effect of VUV irradiation can be partly suppressed by stuffing the low-k porous matrix with proper sacrificial polymers showing high VUV absorption together with good thermal and VUV stability. In addition, the choice of an appropriate hard-mask, showing high VUV absorption, can minimize VUV damage. Particular processing conditions allow to minimize the fluence of photons to the substrate and lead to negligible VUV damage. For patterned structures, in order to reduce VUV damage in the bulk and on feature sidewalls, the combination of both pore stuffing/material densification and absorbing hard-mask is recommended, and/or the use of low VUV-emitting plasma discharge.

Development of a Cu and W Compatible PERR Clean in BEOL Advanced Interconnect Patterning

In back-end of line (BEOL), the fluorinated polymer deposited on dielectric sidewalls during patterning [1,2] must be removed prior to the subsequent processing steps to achieve good adhesion and coverage of materials (metals) deposited in the etched features. Recent results clearly showed the presence of a highly fluorinated layer deposited on the trench sidewalls during the plasma etch using a fluorocarbon based plasma [3]. The challenges related to the wet cleaning of such structures is the efficient removal of post-etch residues (PERR) by showing high selectivity and compatibility towards a variety of new materials exposed to the wet clean chemistry [4]. This study focuses on the use of acidic (pH:0.5-3) and alkaline (pH:8-13.5) aqueous based chemistries that are compatible with W and Cu, respectively. A schematic overview of a BEOL interconnect structure used for the N10 node (22 nm ½ pitch) is shown in Figure 1. The low-k material and hardmask that are used in this work/stack structure are respectively an OSG type of low-k material with a target value of k=2.4 (~20% open porosity) and TiN. Compatibility tests of different alkaline and acidic chemistries have been performed and proven to be compatible with the OSG 2.4 low-k dielectric material. The alkaline chemistries were compatible with Cu, while the acidic chemistries were compatible with W metal. The etch rate behavior of TiN was also checked. Spectroscopic ellipsometry, capacitance measurements (to measure k-value) and sheet resistance measurements were performed for this study. The test vehicle used to check the cleaning efficiency is a 45 nm ½ pitch BEOL trench short loop structure (Figure 2). A layer of low-k dielectric (80 nm) was first deposited on a 300 mm Si wafer, followed by the deposition of a 30 nm oxide HM and TiN layer (~25 nm), and a BARC/193-nm photoresist layer. The TiN layer was first etched using a HBr/Cl2 plasma, followed by the Oxide HM and OSG etch using a C4F8/CF4-based plasma (TEL Tactras). All dies are fully covered with the same type of 45 nm trench structures. A large choice of techniques was selected to characterize the cleaning efficiency of this test vehicle.One of the techniques used to investigate the cleaning of the CFx residue and TiN removal efficiency, is X-ray photoelectron spectroscopy (XPS). From figure 3, it is clear that the alkaline mixture removes almost completely the TiN within 2 min and at the same time the fluorine-containing residues have almost disappeared. The acidic formulated mixture removed TiFx (684.5 eV) completely while the CFx (688.3 eV) residues were only partially removed. A comparison of these acidic and alkaline formulated mixtures with citric acid and a TMAH:H2O2 mixture respectively, results in various cleaning efficiency but none of the commodity chemistries achieved complete removal of CFx and TiFx. The result obtained on a real device structure of 22.5 nm ½ pitch confirms the good performance obtained on the 45 nm ½ pitch BEOL structure. The SEM images shown in Figure 4 give an evidence that both Cu (M1 level) and the porous dielectrics are fully compatible with the chemistry. Electrical results using this alkaline chemistry, show a very good yield for CD lines, MF structure, and via chains will also be presented and discussed. [1] Y. Furukawa et al., Microelectron. Eng., 70, 267 (2003). [2] Q. T. Le et al., J. Electrochem. Soc. 159, H208 (2012). [3] T. Mukherjee et al., ECS Solid-St. Lett. 2, N11-N14 (2013). [4] E.Kesters et al.,Solid State Phenomena, 219, 201 (2015). Figure 1

Development of a novel wafer-probe for in situ measurements of thin film properties

We report a new development of a diagnostic technique, referred to as the wafer probe, which enables us to qualitatively monitor the plasma-induced changes in thin film dielectrics, in-situ and in real time. The wafer probe is an adaptation of the well-established ion flux probe technique, also known as RF biased or pulse biased planar Langmuir probe. This technique utilises the top surface of a tile cut from a multi-layer wafer as the probing area. This technique was successfully used to characterise different plasma conditions and monitor the plasma-induced changes in the thin layers of the tile, e.g. a porous organosilicate-glass low-κ dielectrics. The wafer probe was used to monitor the different effects of an argon and a hydrogen plasma on low-κ dielectrics, as well as to monitor the etch rate and endpoint of an Ar/SF6 plasma.

Mechanical Stability of Porous Low-k Dielectrics

This paper reviews the mechanical and fracture properties of porous ultralow-k dielectrics with the focus on chip package interaction related issues. It is shown that the mechanical and fracture properties of porous ultralow-k dielectric films are closely linked with porosity, pore morphology, network structure and deposition technology, while their fracture properties are also sensitive to reactive species in the environment. The survivability of low-k dielectrics upon integration, package assembly and subsequent reliability tests is therefore a combination of their mechanical stability, fracture properties, the specific mechanical or thermo-mechanical load and environmental effects.

Mechanical property changes in porous low-k dielectric thin films during processing

The design of future generations of Cu-low-k dielectric interconnects with reduced electronic crosstalk often requires engineering materials with an optimal trade off between their dielectric constant and elastic modulus. This is because the benefits associated with the reduction of the dielectric constant by increasing the porosity of materials, for example, can adversely affect their mechanical integrity during processing. By using load-dependent contact-resonance atomic force microscopy, the changes in the elastic modulus of low-k dielectric materials due to processing were accurately measured. These changes were linked to alterations sustained by the structure of low-k dielectric films during processing. A two-phase model was used for quantitative assessments of the elastic modulus changes undergone by the organosilicate skeleton of the structure of porous and pore-filled dielectrics.

Wetting Behavior of Plasma Etch Residue Removal Solutions on Plasma Damaged and Repaired Porous ULK Dielectrics

Porous ultra low constant materials (ULK) for isolation within the interconnect system of integrated circuits are a promising approach to reduce crosstalk and RC-delays due to shrinking feature sizes [1]. Due to their porosity and the integration of carbon rich species like methyl groups into the Si-O-Si backbone of currently fabricated PECVD SiCOH dielectrics those materials are highly sensible towards plasma processing, e.g. dry etching or resist stripping [2]. Metal hard mask approaches, e.g. using TiN hard masks are widely used to prevent the resist stripping plasma directly attacking the low-k material [3]. To reduce further plasma damage like carbon depletion and formation of polar silanol groups the development of less aggressive etching processes is in the focus of research and development activities. Nevertheless dry etching will attack the sidewalls and cause a material degradation. That is why repair processes, mainly based on silylation, are considered to follow the patterning step to reintegrate carbon rich species and to recover the dielectric’s properties [3]. Subsequently to dry etching and repairing the dielectric the wet chemical plasma etch residue removal process is performed. Besides material compatibility and effectiveness in residue removal the wetting behavior of the applied cleaning solutions towards the surface which has to be cleaned is crucial, especially looking on wetting issues like the incomplete wetting of very small via holes or pattern collapse. In this study we investigate in which way different silylation based repair processing regimes are affecting the wettability of the dielectric by water based cleaning solutions using contact angle based surface energy calculations.

Effects of plasma and vacuum-ultraviolet exposure on the mechanical properties of low-k porous organosilicate glass

The effects of plasma exposure and vacuum-ultraviolet (VUV) irradiation on the mechanical properties of low-k porous organosilicate glass (SiCOH) dielectric films were investigated. Nanoindentation measurements were made on SiCOH films before and after exposure to an electron-cyclotron-resonance plasma or a monochromatic synchrotron VUV beam, to determine the changes of film hardness, elastic modulus, and crack threshold due to these exposures. This permits the effects of ion bombardment and photon bombardment to be analyzed separately. The role of energetic ions was examined with a variety of inert plasma-exposure conditions. The role of VUV photons was analyzed as a function of synchrotron photon energy. It was found that both energetic ions and VUV photons with energies larger than the bond energy of the Si-O bond cause a significant increase in film hardness along with a smaller increase in elastic modulus and crack threshold. Differential Fourier transform infrared spectra and x-ray photoemission spectroscopy results show that the energetic ions affect the SiCOH properties mainly through physical bombardment, during which the ions transfer their momentum to the Si-O-Si backbone and transform them into more energetically stable Si-O-Si network structures. This results in the Si-O-Si network structures becoming densified. VUV photons assist reaction that increase the number of bridging O3≡Si-O-Si≡O3 bonds and deplete nonbridging O3≡Si-O and C-Si≡O3 bonds. This increased degree of cross linking in porous organosilicate dielectrics can substantially enhance their hardness and elastic modulus while showing no significant film shrinkage or densification.

A Charge Transport Model for SiCOH Dielectric Breakdown in Copper Interconnects and Its Applications

A charge transport model has been applied to predict dielectric breakdown in copper interconnects. The model very accurately predicts the lifetimes of dense and porous dielectrics over long periods. The predictions of the model significantly vary from currently available methodologies, which fail to adequately account for copper charge transport. We apply this charge transport model to simulate the TDDB lifetime activation energy (E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> , eV) in copper interconnects. The model again very accurately predicts the available activation energy data, in actual interconnect test structures, over a wide range of electric fields. The model can be applied to determine the reliable operating voltage for a given operating temperature.

Bandgap measurements of low-k porous organosilicate dielectrics using vacuum ultraviolet irradiation

Vacuum ultraviolet (VUV) photoemission spectroscopy is used to investigate the effect of VUV radiation on porous organosilicate (SiCOH) dielectrics during plasma processing. By comparing photoemission spectroscopic results before and after VUV exposure, VUV irradiation with photon energies less than 9.0 eV was found to be beneficial in depleting accumulated charge in SiCOH films while VUV photons with higher energies did not have this effect. Moreover, VUV irradiation with 8.9 eV photons depletes the most charge. From this result, it can be concluded that 8.9 eV is the bandgap plus the electron affinity energy of SiCOH dielectrics.