Hualiang Shi

Mechanistic study of plasma damage of low k dielectric surfaces

Plasma damage to low k dielectric materials was investigated from a mechanistic point of view. Low k dielectric films were treated by Ar, O2, N2, N2∕H2, and H2 plasmas in a standard reactive ion etching chamber and the damage was characterized by angle resolved x-ray photoelectron spectroscopy, x-ray reflectivity, Fourier transform infrared spectroscopy, and contact angle measurements. Both carbon depletion and surface densification were observed on the top surface of damaged low k materials while the bulk remained largely unaffected. Plasma damage was found to be a complicated phenomenon involving both chemical and physical effects, depending on chemical reactivity and the energy and mass of the plasma species. A downstream hybrid plasma source with separate ions and atomic radicals was employed to study their respective roles in the plasma damage process. Ions were found to play a more important role in the plasma damage process. The dielectric constant of low k materials can increase up to 20% due to p...

Role of ions, photons, and radicals in inducing plasma damage to ultra low-k dielectrics

The damage induced by CO2 and O2 plasmas to an ultra low-k (ULK) dielectric film with a dielectric constant (κ) of 2.2 was investigated. The dielectric constant was observed to increase due to methyl depletion, moisture uptake, and surface densification. A gap structure was used to delineate the role of ions, photons and radicals in inducing the damage, where the experimental variables included an optical mask (MgF2, fused silica, and Si), a gap height, an inductively coupled plasma power source, a bias power on the bottom electrode, variable chamber pressure, and variable substrate temperature. The plasma radical density distribution inside the gap between the optical mask and the ULK film was simulated. The simulation was based on radical diffusion, reaction, and recombination inside the gap. The experimental results and the numerical simulation showed that the oxygen radicals played an important role in plasma induced damage which was found to be proportional to the oxygen radical density and enhanced ...

Origin of dielectric loss induced by oxygen plasma on organo-silicate glass low-k dielectrics

This study investigated the origin of dielectric loss induced by O2 plasma on organo-silicate glass low-k dielectrics. The contributions from the polarization components to dielectric constant were delineated by analyzing the results from capacitance-voltage measurement, spectroscopic ellipsometry, and Fourier transform infrared spectroscopy together with the Kramers–Kronig dispersion relation. The dielectric loss was found to be dominated by the dipole contribution, compared with the electronic and ionic polarizations. The origin of the dipole contribution was further investigated by performing quantum chemistry calculations. The physisorbed water molecules were found to be primarily responsible for the dipole moment increase and the dielectric loss.

Restoration and pore sealing of plasma damaged porous organosilicate low k dielectrics with phenyl containing agents

Silylation-based techniques are being actively investigated for dielectric recovery after plasma processing of porous ultralow dielectric constant (low k) dielectrics. A two-step pore sealing and dielectric recovery process was attempted on plasma damaged porous organosilicates (OSG). In the sealing step, an OSG low k monomer, phenyltrimethoxysilane, was used to form a thin low k sealant layer. Scanning transmission electron microscopy and transmission electron microscopy images indicated a much improved low k/barrier interface as a result of pore sealing. In the surface silylation step, two phenyl-containing agents, diphenyltetramethyldisilasane and phenyldimethylchlorosilane, were employed to restore surface hydrophobicity. The process was found to be capable of restoring surface hydrophobicity and partially blocking the pathway for moisture adsorption without much adverse effect on the subsequent atomic layer deposition of Cu barrier.

Mechanistic Study of Plasma Damage and CH4 Recovery of Low k Dielectric Surface

A mechanistic study was performed to investigate plasma damage and CFL, recovery of porous carbon-doped oxide (CDO) low k surfaces. First the nature of damage was examined for different plasma treatments in a standard RIE chamber then followed by a study using a downstream hybrid plasma source with separate ions and atomic radicals to investigate their respective roles in the plasma process. Plasma damage was found to be a complicated phenomenon involving both chemical and physical effects, depending on chemical reactivity and the energy and mass of the plasma species. Moisture uptake after plasma damage was found to be a major reason to cause dielectric constant increase. The CFL plasma treatment was found to be promising in repairing oxygen ashing damages by formation of a carbon-rich polymer layer. However, sp2 carbons on the top polymer layer seemed to limit the penetration of plasma CH4 and thus full recovery of low k damage.

Moisture Transport and its Effects on Fracture Strength and Dielectric Constant of Underfill Materials

With continuing demands on increasing die size and device density, underfills are widely used in flip-chip and ball-grid array packages for improvement of reliability. Fracture of the underfill/die interfaces is often observed, particularly at the die corners under a humid environment, raising serious reliability concerns. Moisture uptake can also increase the dielectric constant of underfill materials to degrade the electrical performance of the packages. In this paper, we investigated the diffusion kinetics of moisture and its effects on the fracture energy and effective dielectric constant for two underfill materials. The moisture transport kinetics was studied by a TGA weight loss method and a capacitance measurement method. Based on these results together with diffusion modeling, Arrhenius type relations for moisture diffusion constant and moisture concentration ratio were determined. The interfacial fracture energy of underfills sandwiched by SiN-deposited Si-substrate was measured under various humidity conditions using a double cantilever beam (DCB) method. The crack driving force was systematically reduced by more than 40% as the moisture content increased to saturation in the samples. The locus of failure was cohesive inside underfill materials. Sample preparation technique comprising narrower underfill layer than Si-substrate reduced the incidents of premature failure during testing. Finally, the moisture effect on the increase of dielectric constant was determined using capacitance measurement methods. The dielectric relaxation factor per unit moisture content is reported for the two underfills.

Effect of CH4 Plasma Treatment on O2 Plasma Ashed Organosilicate Low-k Dielectrics

During an O 2 plasma ashing process, carbon depletion and subsequent moisture uptake caused increase of keff and the leakage current in an organosilicate (OSG) low-k dielectric. For dielectric restoration, additional CH 4 plasma treatment on the O 2 plasma ashed OSG low-k dielectric was investigated using angle resolved x-ray photoelectron spectroscopy (ARXPS), XPS depth profiling, x-ray reflectivity (XRR), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and contact angle goniometer. After CH 4 plasma treatment on the O 2 plasma ashed OSG, the surface carbon concentration and surface hydrophobicity were partially recovered. A dense surface layer containing C=C bonds was found to have formed on the top of the damaged OSG. The C-V hysteresis and the leakage current were reduced as a result of the CH 4 plasma treatment. XPS depth profiling revealed that the recovery effect was limited to the surface region.

Mechanistic Study of Plasma Damage of Low k Dielectric Surfaces

Plasma damage to low k dielectric materials was investigated from a mechanistic point of view. Low k dielectric films were treated by plasma Ar, O2, N2/H2, N2 and H2 in a standard RIE chamber and the damage was characterized by Angle Resolved X-ray Photoelectron Spectroscopy (ARXPS), X-Ray Reflectivity (XRR), Fourier Transform Infrared Spectroscopy (FTIR) and Contact Angle measurements. Both carbon depletion and surface densification were observed on the top surface of damaged low k materials while the bulk remained largely unaffected. Plasma damage was found to be a complicated phenomenon involving both chemical and physical effects, depending on chemical reactivity and the energy and mass of the plasma species. A downstream hybrid plasma source with separate ions and atomic radicals was employed to study their respective roles in the plasma damage process. Ions were found to play a more important role in the plasma damage process. The dielectric constant of low k materials can increase up to 20% due to plasma damage and we attributed this to the removal of the methyl group making the low k surface hydrophilic. Annealing was generally effective in mitigating moisture uptake to restore the k value but the recovery was less complete for higher energy plasmas. Quantum chemistry calculation confirmed that physisorbed water in low k materials induces the largest increase of dipole moments in comparison with changes of surface bonding configurations, and is primarily responsible for the dielectric constant increase.

Minimization of plasma ashing damage to OSG low-k dielectrics

This paper investigated the plasma ashing damage to patterned porous low k structures with the objective to minimize the plasma damage by optimizing the low-k structural geometry and plasma chemistry. We first extended the plasma altered layer model to formulate the transport kinetics of the plasma process in patterned low-k structures. This enabled us to analyze the effects of the hardmask thickness, trench width and trench length on the plasma interaction with the trench sidewall. Then CO/O2 and CO2/N2 plasmas were used to replace O2 plasma for ashing process to examine their potential for reducing plasma ashing damage to porous low k patterned structures. With increasing CO in CO/O2 plasma, the extent of plasma induced damages was found to decrease. Similarly, with increasing N2 in CO2/N2 plasma, the plasma induced damages were also found to decrease. On the basis of the Knudsen diffusivity difference among C, N, and O, the reduction of plasma induced damage was ascribed to the formation of C- and N- rich passivation layer on the sidewall and pore surface of the patterned low-k structure.

Plasma altered layer model for plasma damage characterization of porous OSG films

A plasma altered layer model was developed to characterize plasma damage in porous OSG (organosilicate glass) low-k dielectrics by taking into account the kinetics of radical diffusion, reaction, and recombination. A gap structure was designed to study plasma damage and validate the model. It consisted of two parallel rectangular Si spacers and a top optical mask to control the energy and intensity of ion, photon, and radical in the plasma. CO2 and O2 plasma-induced damages were found to depend on the radical concentration, the energy and intensity of VUV photons, the ion energy, and the substrate temperature. Overall, the results obtained from plasma damage studies were consistent with the prediction of the model. The application of the model was demonstrated in a study of He plasma pretreatment and damage formation in OSG films with varying carbon concentrations. Both treatments were found to be effective in improving the material resistance to plasma damage.