Changes to Charge and Defects in Dielectrics from Ion and Photon Fluences during Plasma Exposure

Abstract

A methodology is introduced to investigate the effects of ion and photon fluences on dielectrics during plasma exposure. Ion and photon fluences were separated using a capillary-array window. The fluences can be varied separately by varying the plasma parameters. Most of the charge accumulation came from the ion fluence, while the photon fluence introduced most of the defect-state modifications. It was further shown that during plasma exposure, UV photons can penetrate through the dielectric layer and cause modifications of the defect states. Based on the results, optimized conditions were found to minimize both the charge accumulation and the defect-state formation during plasma exposure.Plasma-processing-induced damage has been an important issue in manufacturing microelectronic devices. 1 Damage includes dielectric charging, 2 defect-state formation, 3,4 chemical and physical changes, 5,6 and mechanical degradation. 7 This processing-induced damage can be from ions, photons, and radicals striking the dielectric. 8,9 Among these damage sources, ion bombardment has been believed to be the greatest for changing the properties of dielectrics. 8 However, such ion-induced damage may only happen within an ion penetration depth. 10 Vacuum ultraviolet ͑VUV͒-modified dielectric layers were typically shown to be deeper than the ion-modified layer. 11 Based on this, it is our contention that, within the dielectric, beyond the ion penetration depth, photons are responsible for the damage in this region, while on the surface, the damage is primarily caused by ions. Here, the two sources of damage generated during plasma processing will be considered to determine the effects of ion and photon fluences on the damage. They are charge accumulation and defect-state formation. This article establishes the roles of photons and ions in charge accumulation and defect-state formation in dielectric materials.In order to determine this, electron-spin resonance ͑ESR͒ spectroscopy measurements were made to detect the modifications of the interfacial defect states and surface potential measurements with a Kelvin probe were used to detect the charge accumulation. Previously, VUV and UV exposures from synchrotron radiation and HgAr lamp have been shown to be responsible for the interlayer defect-state modifications in the dielectrics. 12 As a test sample, we used atomic-layer-deposited 20-nm-thick HfO 2 on ͑100͒Si. Note that the dielectric sample is ultrathin which guarantees a modification of the interfacial defects. The resistivity of silicon substrate is 4000 ⍀ cm which is needed to obtain effective ESR measurements. 13 An electron cyclotron resonance plasma system 9 was utilized to provide the plasma exposure of the dielectric films. Argon plasma was used to minimize the creation of free radicals, 14 so that the ion and photon bombardments were the primary sources of potential damage.To vary the ion and photon fluences, pressure and microwave power were scanned between ranges of 5 and 30 mTorr and 100 and 400 W, respectively. The pressu...

Plasma-Assisted Atomic Layer Deposition: Basics, Opportunities, and Challenges

“…The bombardment of the substrate by energetic ions, accelerated in the plasma sheath, can lead to bond-breaking, displacement of atoms in the surface region and charge accumulation on dielectric layers. 344,345 Such ion bombardment effects are particularly important during plasma-activated processes, such as reactive ion etching, where the substrate is negatively biased to give the incoming ions kinetic energies of up to several hundreds of eV. 299,300 During plasma-assisted ALD the ion energies are typically much lower due to grounding of the substrate stage and/or the high pressures employed (i.e., when the plasma sheath is collisional), meaning that they are typically below the damage threshold (e.g.…”

“…Plasma-induced defect creation has been studied in great detail for the plasma processing of SiO 2 -based gate stacks 299,300,[346][347][348][349] and the influence of VUV exposure has also recently been studied for the high-k oxide HfO 2 . 299,300,344,[350][351][352] However, this damage mechanism has not really been highlighted for plasma-assisted ALD processes, for example, during the synthesis of metal oxides by plasma-assisted ALD itself or when depositing other materials (such as electrode materials) on top of high-k oxides by plasma-assisted ALD. Note that, apart from the fact that the metal oxide film might itself be affected, the interfacial SiO x layer, which is typically present (either unintentionally or prepared on purpose) between the metal oxide and the Si substrate, can also be affected.…”

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

“…14 The exposure time for each sample was set to be 5 min at 20 mTorr argon neutral pressure. The ion flux, measured using a Langmuir probe as described previously, 25 was determined to be 1. As shown in Figure 3, the energetic ions from the plasma collide with the dielectric surface and physically bombard the backbone bonds.…”

“…This is the case even through an energy of 6.1 eV is higher than the bond strength of the C-Si bond, whose dissociation energy is 4.5 eV. 25 Prager et al 29 pointed out that only VUV irradiation with wavelengths less than 190 nm (E photon > 6.5 eV) can break the H 3 C-Si bonds and generate Si-centered radicals which subsequently attract protons from neighboring groups. This explains why there is no experimentally observed mechanical property change in SiCOH after exposure to 6.1 eV photons.…”

Measuring the volume charge in dielectric films using single frequency electro-acoustic waves

“…1 However, measuring the distribution perpendicular to the surface is much more challenging, especially as the thickness of the film decreases into the submicron range. Potential measurement techniques have been studied since the 1970s, and several different methods have been developed.…”