Jasbir S. Juneja

Very low-refractive-index optical thin films consisting of an array of SiO 2 nanorods

The refractive-index contrast in dielectric multilayer structures, optical resonators, and photonic crystals is an important figure of merit that creates a strong demand for high-quality thin films with a low refractive index. A SiO2 nanorod layer with low refractive index of n = 1.08, to our knowledge the lowest ever reported in thin-film materials, is grown by oblique-angle electron-beam deposition of SiO2. A single-pair distributed Bragg reflector employing a SiO2 nanorod layer is demonstrated to have enhanced reflectivity, showing the great potential of low-refractive-index films for applications in photonic structures and devices.

Pressure dependent Parylene-N pore sealant penetration in porous low-κ dielectrics

The introduction of porosity in dielectrics is desirable to reduce the dielectric constant; but it causes integration problems such as CVD∕ALD precursor penetration for barrier layer∕seed layer deposition. CVD Parylene-N has been shown to work as a pore sealant for porous low-κ materials but penetrates itself slightly into porous dielectric. The depth profile of Parylene-N in porous MSQ can be obtained using the Nuclear Reaction Analysis (NRA) of C12. The penetration of Parylene-N can be controlled by deposition at higher pressure where the deposition rate is also high. High deposition rate can also be attained by adding a carrier gas which also shows low Parylene-N penetration. The experimentally measured dielectric constants, after pore sealing, are compared to those calculated using the NRA data of Parylene-N penetration.

Instability of Metal Barrier with Porous Methyl Silsesquioxane Films

Integration of porous ultralow-K dielectrics into advanced copper interconnect scheme has been a challenge. Among other issues, metal diffusion/drift into interconnected pores consequently leading to the degradation of dielectrics is a concern. In the present work, the electrical stability of the metal-insulator-semiconductor (MIS) capacitors with various metal electrodes on porous methyl silsesquioxane (MSQ) on thermal oxide/n-type silicon was investigated. Our results suggest that the tendency of various metal, Pt < Cu < Ru < Ta < Al, drift into porous MSQ under bias-temperature stress (BTS) corresponds to the order of metal oxidation tendency at the interface. It is noted that the metal barrier materials such as Ta and Ru perform worse than Cu itself. This behavior is similar to metal drift in organosiloxane polymer reported earlier [Appl. Phys. Lett., 79, 1855 (2001)]. Furthermore, as-prepared MIS capacitors with Cu electrodes show stable capacitance-voltage characteristics under a moderate BTS of 150°C and 0.5 MV/cm. Under the same BTS, a deterioration of the MIS capacitors with increasing exposure time in air is observed. The electrical stability is fully restored after being annealed at an elevated temperature of 350°C in a reducing ambient. The degradation of the MIS capacitors over time is attributed to the permeation of oxygen and moisture through interconnected pores, which consequently facilitate the formation of interfacial Cu oxide. The electrical stability of MIS capacitors with Ta electrodes however does not exhibit improvement by such annealing because of their greater heat of oxide formation. The MIS capacitors with Al electrodes on N 2 O-plasma treated porous MSQ show less metal drift than Al on porous MSQ, suggesting that the intrinsic property of metal oxide determines whether the oxygen contained in the dielectrics assists or inhibits the metal-related activities.

Effects of substrate temperature on properties of pulsed dc reactively sputtered tantalum oxide films

The effects of substrate heating on the stoichiometry and the electrical properties of pulsed dc reactively sputtered tantalum oxide films over a range of film thickness (0.14to5.4μm) are discussed. The film stoichiometry, and hence the electrical properties, of tantalum oxide films; e.g., breakdown field, leakage current density, dielectric constant, and dielectric loss are compared for two different cases: (a) when no intentional substrate/film cooling is provided, and (b) when the substrate is water cooled during deposition. All other operating conditions are the same, and the film thickness is directly related to deposition time. The tantalum oxide films deposited on the water-cooled substrates are stoichiometric, and exhibit excellent electrical properties over the entire range of film thickness. “Noncooled” tantalum oxide films are stoichiometric up to ∼1μm film thickness, beyond that the deposited oxide is increasingly nonstoichiometric. The presence of partially oxidized Ta in thicker (>∼1μm) nonc...

Enhancement of Cu ( hfac ) 2 Chemisorption on the Parylene Surface by N2 Plasma Surface Modification

We show that N 2 plasma treatment introduces both nitrogen and oxygen functional groups onto the Parylene surface without significantly changing the Parylene surface morphology. X-ray photoelectron spectroscopy (XPS) analyses reveal that there is more copper(II) bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionate) [Cu(hfac) 2 ] adsorbed on the plasma-treated Parylene surface than on the untreated Parylene surface, which indicates that the chemisorption of Cu(hfac) 2 on the Parylene surface is enhanced by its interaction with the existing functional groups. The Cu(hfac) 2 interacts with functional groups via the transfer of H atoms to hfac ligands, resulting in the formation of volatile Hhfac. The F Is XPS spectrum observed on the Parylene surface after being exposed to the Cu(hfac) 2 precursor suggests that the hfac ligands are still attached to Cu. The binding energy of Cu 2p 3/2 observed in the XPS spectra is in the range 934.4-935.3 eV, which is higher than that of bulk metallic Cu (932.4 eV) and closer to the Cu (II) oxidation state.

Bias-Temperature Stability of Ti–Si–N–O Films

Copper shows a tendency to drift into contiguous dielectric material under bias and temperature stressing. The stability of different compositions (by changing silane gas flow rate) of Ti-Si-N-O films has been investigated using metal-oxide-semiconductor (MOS) capacitors. MOS samples preannealed at 250°C and subjected to bias temperature stressing (BTS) at 150°C, 200°C under an electrical field of 0.5 or 1 MV/cm show stable capacitance-voltage behavior with no flatband voltage shift from as-annealed to 90 min of BTS for Ti-Si-N-O film with Si/Ti ratio of 0.48. The lack of flatband voltage shift indicates that Ti-Si-N-O film is able to prevent Cu ion penetration. It is found that the electrical stability of Ti-Si-N-O film is reduced with higher Si/Ti ratio. For Ti-Si-N-O film with Si/Ti ratio of 0.91, flatband voltage shifts 0.75 V after 90 min of BTS at 150°C and 0.5 MV/cm, and this shift is attributed to the interface states at the Ti-Si-N-O/oxide interface that were generated during the plasma process and could not be fully healed after 250°C annealing. Thus, it is suggested that with low silane gas flow rate, an electrically stable Ti-Si-N-O film can be achieved with fewer interface states.

Novel Epoxy Siloxane Polymer as Low-K Dielectric

This paper introduces a low-k dielectric material, a novel epoxy siloxane polymer, made by Polyset Co. Inc, which has promising properties. The polymer was spin-deposited, and thickness and optical properties were measured using variable-angle spectroscopic ellipsometry (VASE). Fourier transform infrared (FTIR) spectra of as deposited and cured polymers showed that the polymer is fully cured at 165 °C. The low curing temperature of the polymer lowers stress in back-end-of-line (BEOL) stack and thus improves the reliability. The polymer is thermally stable up to 400 °C. The polymer has Youngs modulus of ∼5 GPa and hardness of greater than 0.4 GPa. After multiple stress cycles up to 300 °C, the residual stress in the polymer at room temperature is less than 60 Mpa. The polymer has good adhesion with semiconductor and dielectrics such as Si, SiC, and SiO 2 , metals such as Al, Cu, Co, and W, and barrier materials such as TaN. The bulk dielectric constant of the polymer is 2.4 - 2.7. The leakage current density in the polymer at the applied electrical field of 1 MV/cm is in 10 −9 A/cm 2 range and the breakdown field of the polymer is ranging from 5 to 7 MV/cm. The polymer when subjected to bias-temperature stress (BTS) conditions of 150 °C and 0.5 MV/cm shows no C-V shift for up to 100 min indicating that the polymer resists Copper diffusion. The current density under stress conditions of 150 °C and 0.5 MV/cm was less than 10 −9 A/cm 2 for up to 7 hrs.

Copper drift in high-dielectric-constant tantalum oxide thin films under bias temperature stress

The use of high-dielectric-constant (high-κ) materials for embedded capacitors is becoming increasingly important. Tantalum oxide (Ta2O5) is a prominent candidate as a high-κ material for embedded capacitor use. Metal drift in Ta2O5 (κ∼25) was investigated by bias temperature stress and triangular voltage sweep testing techniques on metal/Ta2O5∕SiO2∕Si structures. At a temperature of 300°C and 0.75MV∕cm bias conditions, Al, Ta, and Ti do not diffuse in Ta2O5, but Cu clearly showed a drift. The Cu drift is attributed to the lack of a stable Cu oxide which can limit Cu ion generation and penetration.

Dry etching, surface passivation and capping processes for antimonide based photodetectors

III-V antimonide based devices suffer from leakage currents. Surface passivation and subsequent capping of the surfaces are absolutely essential for any practical applicability of antimonide based devices. The quest for a suitable surface passivation technology is still on. In this paper, we will present some of the promising recent developments in this area based on dry etching of GaSb based homojunction photodiodes structures followed by various passivation and capping schemes. We have developed a damage-free, universal dry etching recipe based on unique ratios of Cl2/BCl3/CH4/Ar/H2 in ECR plasma. This novel dry plasma process etches all III-V compounds at different rates with minimal damage to the side walls. In GaSb based photodiodes, an order of magnitude lower leakage current, improved ideality factor and higher responsivity has been demonstrated using this recipe compared to widely used Cl2/Ar and wet chemical etch recipes. The dynamic zero bias resistance-area product of the Cl2/BCl3/CH4/Ar/H2 etched diodes (830 Ω cm2) is higher than the Cl2/Ar (300 Ω cm2) and wet etched (330 Ω cm2) diodes. Ammonium sulfide has been known to passivate surfaces of III-V compounds. In GaSb photodiodes, the leakage current density reduces by a factor of 3 upon sulfur passivation using ammonium sulfide. However, device performance degrades over a period of time in the absence of any capping or protective layer. Silicon Nitride has been used as a cap layer by various researchers. We have found that by using silicon nitride caps, the devices exhibit higher leakage than unpassivated devices probably due to plasma damage during SiNx deposition. We have experimented with various polymers for capping material. It has been observed that ammonium sulfide passivation when combined with parylene capping layer (150 Å), devices retain their improved performance for over 4 months.

Interfacial interaction of in situ Cu growth on tetrasulfide self-assembled monolayer on plasma treated parylene surface

The interfacial reactions of in situ grown Cu and functionalized parylene surfaces were examined using the x-ray photoelectron spectroscopy (XPS). It is observed that bis[3(triethoxysilane)propyl]tetrasulfide (tetrasulfide) forms a self-assembled monolayer (SAM) only on a parylene surface treated with either He plasma or N2 plasma, but not on the as-deposited parylene surface due to its lack of functional groups. The functional groups on the plasma treated parylene surface facilitate the formation of tetrasulfide SAM that subsequently improves the reactivity of parylene to Cu. The XPS spectra show a strong shift (∼1.1eV) of the S 2p peaks from a higher binding energy to a lower binding energy, which suggests the existence of an interaction between sulfide and Cu. In addition, the result of a higher XPS intensity ratio of Cu 2p3∕2∕C 1s for Cu growth on tetrasulfide SAM/plasma treated parylene surface than that of an as-deposited parylene surface indicates that the formation of tetrasulfide moiety (–SSSS–) ...