Intermetal Dielectric Materials Research Articles

Exploring thermal effects of advanced backside power delivery network beyond 3 nm node

Backside Power Delivery Networks (BSPDNs) address scaling issues by relocating power, boosting efficiency and density. However, thermal effects pose challenges. In this work, a comprehensive thermal analysis of BSPDN is performed to elaborate the key modulation factors and possible optimization approaches, where the specific backside metal layers are constructed to investigate the impacts of operating conditions, via distribution and materials on thermal effects. To improve the simulation efficiency, the effective thermal conductivity is employed to simplify the Nanosheet (NSH) FET based front-end-of-line (FEOL) and other layers at the 3 nm technology node. Results show that non-uniform via distribution in BSPDN causes temperature fluctuations, but augmenting Backside Via counts effectively mitigates local peak temperature increases from higher power. For BSPDN, backside cooling solutions outperform frontside in efficiency, particularly at high via densities. Using high thermal conductivity inter-metal dielectric (IMD) materials significantly reduces global temperature rise and fluctuations from non-uniform vias in BSPDN, enhancing PDN design flexibility.

Change in Electrical/Mechanical Properties of Plasma Polymerized Low Dielectric Constant Films after Etching in CF4/O2 Plasma for Semiconductor Multilevel Interconnects.

As semiconductor chips have been integrated to enhance their performance, a low-dielectric-constant material, SiCOH, with a relative dielectric constant k ≤ 3.5 has been widely used as an intermetal dielectric (IMD) material in multilevel interconnects to reduce the resistance-capacitance delay. Plasma-polymerized tetrakis(trimethylsilyoxy)silane (ppTTMSS) films were created using capacitively coupled plasma-enhanced chemical vapor deposition with deposition plasma powers ranging from 20 to 60 W and then etched in CF4/O2 plasma using reactive ion etching. No significant changes were observed in the Fourier-transform infrared spectroscopy (FTIR) spectra of the ppTTMSS films after etching. The refractive index and dielectric constant were also maintained. As the deposition plasma power increased, the hardness and elastic modulus increased with increasing ppTTMSS film density. The X-ray photoelectron spectroscopy (XPS) spectra analysis showed that the oxygen concentration increased but the carbon concentration decreased after etching owing to the reaction between the plasma and film surface. With an increase in the deposition plasma power, the hardness and elastic modulus increased from 1.06 to 8.56 GPa and from 6.16 to 52.45 GPa. This result satisfies the hardness and elastic modulus exceeding 0.7 and 5.0 GPa, which are required for the chemical-mechanical polishing process in semiconductor multilevel interconnects. Furthermore, all leakage-current densities of the as-deposited and etched ppTTMSS films were measured below 10-6 A/cm2 at 1 MV/cm, which is generally acceptable for IMD materials.

Study on Effects of Carrier Gas Flow Rate on Properties of Low Dielectric Constant Film Deposited by Plasma Enhanced Chemical Vapor Deposition Using the Octamethylcyclotetrasiloxane Precursor.

In semiconductor industry, low-dielectric-constant SiCOH films are widely used as inter-metal dielectric (IMD) material to reduce a resistance-capacitance delay, which could degrade performances of semiconductor chips. Plasma enhanced chemical vapor deposition (PECVD) system has been employed to fabricate the low-dielectric-constant SiCOH films. In this work, among various parameters (plasma power, deposition pressure, substrate temperature, precursor injection flow rate, etc.), helium carrier gas flow rate was used to modulate the properties of the low-dielectric-constant SiCOH films. Octamethylcyclotetrasiloxane (OMCTS) precursor and helium were injected into the process chamber of PECVD. And then SiCOH films were deposited varying helium carrier gas flow rate. As helium carrier gas flow rate increased from 1500 to 5000 sccm, refractive indices were increased from 1.389 to 1.428 with enhancement of mechanical strength, i.e., increased hardness and elastic modulus from 1.7 and 9.1 GPa to 3.3 and 19.8 GPa, respectively. However, the relative dielectric constant (k) value was slightly increased from 2.72 to 2.97. Through analysis of Fourier transform infrared (FTIR) spectroscopy, the effects of the helium carrier gas flow rate on chemical structure, were investigated. It was thought that the increase in helium carrier gas flow rate could affect the density with changes of chemical structure and composition. In conclusion, regulation of helium carrier gas flow rate can effectively modulate k values and mechanical strength, which is needed for IMD material in semiconductor fabrication possess.

Ultralow dielectric constant SiCOH films by plasma enhanced chemical vapor deposition of decamethylcyclopentasiloxane and tetrakis(trimethylsilyloxy)silane precursors

In semiconductor industry, SiCOH films with low dielectric constant (relative dielectric constant k ≤ 4.0) have been widely used as inter-metal dielectric (IMD) materials in the interconnects of semiconductor chips, to reduce a resistance-capacitance delay. In this study, copolymerized SiCOH films were deposited using the plasma enhanced chemical vapor deposition of decamethylcyclopentasiloxane (DMCPS) and tetrakis(trimethylsilyloxy)silane (TTMSS) precursors. The chemical structure and materials performances of the SiCOH films strongly depended on the flow rate ratios (FRRs) of DMCPS/TTMSS. The chemical bonds and compositions of the SiCOH films were investigated using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The peak area ratios of methyl groups (CH3)x (x=1,2,3) in the spectra varied with the FRRs, affecting the k values and mechanical strengths of the films. The SiCOH films with the FRR of 1.0 showed the elastic modulus of 8.27 GPa and hardness of 0.96 GPa, which are acceptable values for semiconductor devices manufacturing. Ultralow-k values below 2.5 were achieved, along with the leakage current density below 10−6 A•cm−2 at 1 MV•cm−1. The enhanced mechanical and electrical performance with the appropriate FRR of DMCPS/TTMSS suggest the possibility of applying the copolymerized SiCOH films as IMD materials.

Development of MEMS MOS gas sensors with CMOS compatible PECVD inter-metal passivation

Metal oxide semiconductor (MOS) based micro-electromechanical sensors (MEMS) for gas measurement were developed using back-end-of-line (BEOL) compatible inter-metal dielectric films deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD). As MOS MEMS require sintering above 600°C, a set of PECVD silicon oxide and nitride films was characterized before and after annealing up to 700°C, in order to identify the best candidate inter-metal dielectric materials. The effect of thermal load on the films was determined by measuring stress, thickness and refractive index after annealing both in dry air and nitrogen atmosphere. Nano-indentation was used to estimate the elastic modulus after annealing. The best performing films were employed as inter-metal dielectric in the full fabrication of microheater MEMS gas sensors. Among the selected films, only silicon oxide deposited with high frequency plasma generator allowed for the complete gas sensor fabrication with no damage. SnO2 paste was successfully screen printed on the fabricated membranes and sintered to enable gas sensing. Electrical and gas sensing tests were performed with the fabricated microheaters, demonstrating full functionality. Thermal stress endurance tests were also conducted, with no membrane deformation after more than 500,000 duty cycles. Results show that the proposed PECVD passivation is compliant up to 650°C firing temperature and 450°C operating temperature, and demonstrate the use of CMOS-BEOL PECVD inter-metal passivation for MOS MEMS gas sensor fabrication.

A method for alleviating the effect of pinhole defects in inter-metal dielectric films

As the insulation layers between two metal layers, inter-metal dielectric (IMD) films are widely used in integrated circuits (IC) and micro-electromechanical-systems (MEMS) devices. Commonly used IMD materials, such as silicon dioxide and silicon nitride, can be deposited on the metal surface using either physical vapor deposition (PVD) or chemical vapor deposition (CVD). However, due to the imperfections of deposition processes and surface cleanliness, defect-free of an IMD film cannot be guaranteed. As a common defect of an IMD film, pinhole is a tiny via of IMD film that can result in failures of short-circuit or current leakage between two metal layers and therefore decrease the fabrication yield. Reported methods for healing the pinhole defect require light-transmitting substrate, suspended structures, high-temperature annealing processes and none of them is universal. Therefore, we propose a metal etching method that uses metal etchants to etch the underlying metals through the pinholes of the IMD film. The etched area is reasonably larger than the pinhole; therefore, although the following upper metal deposition fills the pinhole, there is no electrical connection between the lower and upper metal features through the pinhole. Results of a series of experiments prove that the proposed method is feasible, valid, operable and reliable. Therefore, the proposed method is promising to be used for many IMD-based applications for either discovering pinholes or healing pinhole induced defects.

Effect of K+ ion on the dielectric properties of metallo organic L-alanine cadmium chloride single crystals

The single crystals of pure and Potassium doped L-alanine cadmium chloride (LACC), a metallo organic nonlinear optical material is grown by a slow evaporation technique. The grown crystals were confirmed by single crystal, powder XRD analyses and atomic absorption studies. Dielectric measurements were carried out for different frequencies at different temperatures. The dielectric constant decreases due to the introduction of large ionic radius K+ ion in the pure LACC crystal. The low dielectric constant and dielectric loss suggest that it can be used as inter-metal dielectric material.

0.13μm Cu/Low-k 공정 Setup과 수율 향상에 관한 연구

In this study, the inter-metal dielectric material of FSG was changed by low-k material in <TEX>$0.13{\mu}m$</TEX> foundry-compatible technology (FCT) device process based on fluorinated silicate glass (FSG). Black diamond (BD) was used as a low-k material with a dielectric constant of 2.95 for optimization and yield-improvement of the low-k based device process. For yield-improvement in low-k based device process, some problems such as photoresist (PR) poisoning, damage of low-k in etch/ash/cleaning process, and chemical mechanical planarization (CMP) delamination must be solved. The PR poisoning was not observed in BD based device. The pressure in CMP process decreased to 2.8 psi to remove the CMP delamination for Cu-CMP and USG-CMP. <TEX>$H_2O$</TEX> ashing process was selected instead of <TEX>$O_2$</TEX> ashing process due to the lowest condition of low-k damage. NE14 cleaning after ashing process lot the removal of organic residues in vias and trenches was employed for wet process instead of dilute HF (DHF) process. The similar-state of SRAM yield was obtained in Cu/low-k process compared with the conventional <TEX>$0.13{\mu}m$</TEX> FCT device by the optimization of these process conditions.

Comparison of Optical Properties in Al- and Cu-BEOL of CMOS Image Sensor Devices

Two-dimensional optical simulation and experiments have been performed to investigate light propagation through a microlens and intermetal dielectric (IMD) layers in an Al and Cu back-end of line (BEOL) onto a Si photodiode, and its effects on the wave power, as well as optical carriers generated by a visible ray in the Si substrate area, i.e., photodiode of complementary metal oxide semiconductor (CMOS) image sensor (CIS) pixel. It is shown that more optical carriers are generated in the Cu-BEOL for the red color due to the use of higher permittivity SiC in the Cu-BEOL to prevent Cu from diffusing into the dielectric material, resulting in higher optical loss in the higher-permittivity dielectric layers. Thus, the optical power density arriving in the Si substrate is higher in the Al-BEOL than in the Cu-BEOL when the wavelength is blue (470 nm) or green (550 nm) in the visible ray spectrum. Therefore, the structure of a Cu-BEOL in a CIS must be optimized for generating more optical carriers through lower-permittivity IMD materials or by reducing the permittivity difference between SiC (or SiN) and IMD materials without deteriorating the capability as a barrier to Cu diffusion.

Characterization of Chemical Bonding in Low-K Dielectric Materials for Interconnect Isolation: A XAS and EELS Study

AbstractThe use of low dielectric constant materials in the on-chip interconnect process reduces interconnect delay, power dissipation and crosstalk noise. To achieve the requirements of the ITRS for 2007-2009 minimal sidewall damage from etch, ash or cleans is required. In chemical vapor deposited (CVD) organo-silicate glass (OSG) which are used as intermetal dielectric (IMD) materials the substitution of oxygen in SiO2 by methyl groups (-CH3) reduces the permit-tivity significantly (from 4.0 in SiO2 to 2.6-3.3 in the OSG), since the electronic polarizability is lower for Si-C bonds than for Si-O bonds.However, plasma processing for resist stripping, trench etching and post-etch cleaning removes C and H containing molecular groups from the near-surface layer of OSG. Therefore, compositional analysis and chemical bonding characterization of structured IMD films with nanometer resolution is necessary for process optimization.OSG thin films as-deposited and after plasma treatment are studied using X-ray absorp-tion spectroscopy (XAS) and electron energy loss spectroscopy (EELS). In both techniques, the fine structure near the C1s absorption or energy loss edge, respectively, allows to identify C-H, C-C, and C-O bonds. This gives the opportunity to differentiate between individual low-k mate-rials and their modifications. The O1s signal is less selective to individual bonds. XAS spectra have been recorded for non-patterned films and EELS spectra for patterned structures. The chemical bonding is compared for as-deposited and plasma-treated low-k materials. The Fluo-rescence Yield (FY) and the Total Electron Yield (TEY) recorded while XAS measurement are compared. Examination of the C 1s near-edge structures reveal a modified bonding of the re-maining C atoms in the plasma-treated sample regions.

Characterization and thermal stability of fluorosilicate glass films deposited by high density plasma chemical vapor deposition with different bias power

High-density plasma chemical vapor deposition (HDP-CVD) fluorosilicate glass (FSG) films were evaluated for the application of inter-metal dielectric (IMD) materials in current devices. Film characteristics were examined as a function of deposition/sputter etch (D/S) ratio, which was controlled by the bias power in HDP-CVD. FTIR spectra show that the positions of Si–O and Si–F peaks are independent of the bias power, but the Si–O shifted to a higher wave number and Si–F 2 appeared upon annealing for the films deposited at lower bias power. Stress hysteresis of the FSG films after the first thermal cycle shows a nonequilibrium nature of the microstructure related to impurity content, especially for the film deposited with lower bias power. Thermal desorption of H 2O, F, O 2 and Ar were examined, while most of the desorption behaviour can be related to the physical pore structure and pore quantity.

Characterization of sputter-induced temperature effect in fluorine doped SiO 2 film deposition by high-density plasma chemical vapor deposition

High-density plasma chemical vapor deposited fluorosilicate glass (FSG) has been successfully used for the inter-metal dielectric material in ultra-large semiconductor integration manufacturing due to its low-dielectric constant and stable gap-filling capability. However, temperatures rise and related effects due to sputter etch from the deposition process have become major concerns for film properties. In this paper, an independent helium-cooling system was employed to control a suitable temperature range from 410 °C to 460 °C during FSG deposition. Subsequently, film properties including fluorine concentration, distribution, refractive index, dielectric constant and gap-filling capability were thus examined as a function of He pressure used in the cooling system. The results show that both deposition rate and fluorine concentration increase with increasing helium pressure; however, more fluorine becomes inactive, which might be present as defects. We have shown that an FSG film with a dielectric constant down to 3.43 as well as good gap-filling capability can be achieved when employing this new cooling system with 9 mTorr helium pressure.

Enhancement of mechanical properties of organosilicon thin films deposited from diethylsilane

A strong demand exists for improved low-k intermetal dielectric materials, such as organosilicons, to enhance the performance of ultralarge scale integrated circuits. Pulsed-plasma enhanced chemical vapor deposition was used to deposit organosilicon thin films from diethylsilane and oxygen. Fourier-transform infrared (FTIR) analysis showed significant organic content as well as hydroxyl and silanol moieties in the as-deposited materials. FTIR showed a complete removal of hydroxyl groups after annealing at 400°C for 1h. This removal indicates a condensation reaction between proximal hydroxyl groups leading to the formation of additional Si–O–Si linkages, which would increase both the hardness and modulus of the film. Mechanical property measurements were in accordance with this hypothesis, as both the hardness and modulus increased by over 50% after annealing. Film structure and properties were strongly dependent on the precursor feed ratio.

Chemical vapor deposition–physical vapor deposition aluminum plug process for dynamic random-access memory applications

The integrated chemical vapor deposition (CVD)–physical vapor deposition (PVD) Al plug process was successfully applied to capacitor-over-bit-line-type dynamic random-access memory process flow for the simultaneous formation of plugs and wires. The CVD-PVD Al film completely filled re-entrant vias with aspect ratios up to 10:1, and Al plugs showed lower via resistance compared with that of conventional W plugs. The PVD Al temperature can be as low as 350 °C, which is compatible with most low-dielectric-constant intermetal dielectric materials. However, outgassing from the intermetal dielectric was critical to complete via filling of the CVD-PVD Al film, and the conventional degassing process was insufficient for eliminating outgassing from hydrogen silsesquioxane. Sufficient baking after the via etching was effective for eliminating outgassing, and complete via filling was achieved.

The search for low-/spl epsiv/ and ultra-low-/spl epsiv/ dielectrics: how far can you get with polymers? Part 2: materials, structures, properties

The need for continuing miniaturization of the structures on microchips has always resulted in new challenges concerning materials properties. A large variety of polymers have been proposed for this application, as organic materials are among those with the lowest dielectric constants known. The chemical structures and selected properties of these polymers are discussed in this review. Polymides; heteroaromatic polymers; polyaryl ethers; fluoropolymers, polyarylenes, and other hydrocarbon polymers without any polar groups; films deposited from the gas phase by chemical vapor deposition (CVD); plasma-enhanced CVD (PECVD); and other techniques are included. Based on the properties described and the requirements for application as intermetal dielectric (IMD) material, conclusions regarding the possibilities for further developments are draw. This article focuses on the structure, synthesis, and properties of the polymers studied as ILD/IMD materials.

Modeling of N&amp;lt;tex&amp;gt;$_2$&amp;lt;/tex&amp;gt;–H&amp;lt;tex&amp;gt;$_2$&amp;lt;/tex&amp;gt;Capacitively Coupled Plasma for Low-k Material Etching

As the scale of semiconductors shrinks and the interconnect layer develops to tens level, the resistance-capacitance ( RC) delay of signals through interconnection materials becomes a big obstacle for high-speed operation of integrated circuits. In order to reduce the RC delay, low-k materials will be used for intermetal dielectric (IMD) materials. As a result, new etching conditions must be developed to match the material properties. We present the modeling results of a two-frequency capacitively coupled plasma (2f-CCP) with N/sub 2/-H/sub 2/ gas mixture, which is known as a promising one for organic low-k materials etching. We have developed a self-consistent simulation tool which includes neutral-species transport model, based on the relaxation continuum (RCT) model. Not only the plasma transport and spatial distribution, but also those of neutrals are important issues for the etching process. For the etching of low-k materials by N/sub 2/-H/sub 2/ plasma, N and H atoms have a big influence on the materials. Moreover, the distributions of excited neutral species influence the plasma density and profile. Therefore, we include the neutral transport model as well as plasma one in the calculation. The plasma and neutrals are calculated self-consistently by iterating the simulation of both species until a spatiotemporal steady-state profile could be obtained. In the simulation of neutral species, the interactions of excited states and vibrational levels of both N/sub 2/ and H/sub 2/ molecules are considered too. The profiles of periodic steady-state plasma and neutrals species in the 2f-CCP system is discussed.

Chemical vapor deposition of copper thin films for multi-level interconnections

Copper thin films were prepared by a metal organic chemical vapor deposition technology on top of TiN/Si substrates, and the films were examined by varying the experimental substrate temperature and copper source vapor pressure. Emerging semiconductor sub-quarter-micron technologies require a multi-level interconnection design that reduces the interconnection lengths and enhances device speeds. The microstructures of the Cu film were analyzed by transmission electron microscopy and transmission electron diffraction (TEM/TED) and the electrical resistance was measured by a four-point probe. The crystallinity of the Cu films increased as the substrate reaction temperature increased. The optimum reaction temperature was 180 °C. The effect of annealing on the electrical conductivity of the Cu films was also determined. The results indicate that the grain size and crystallinity of the films were observed to increase post-annealing, and thus the electrical conductivity was increased. The optimum electrical property of the copper film was obtained by in-situ annealing treatment at >350 °C for a sample prepared at 180 °C substrate temperature. This technology is suitable for multi-level interconnections in ultra-large-scale integration, since intermetal dielectric materials require low-temperature processes.

Submicron Via-Hole Filling using Al Low-Pressure Seed Process

The submicron via-hole filling using a two-step Al sputtering process which consists of an Al low-pressure seed (ALPS) process and physical vapor deposition (PVD) Al, is described in this paper. The effect of the type of intermetal dielectric (IMD) material used, such as hydrogen silsesquioxane (HSQ), high-density plasma (HDP) oxide, and siloxane silicon-on-glass (SOG), on the via esistance and via-hole filling capability was evaluated and discussed. The Al film behavior after ALPS deposition, preheating, and PVD Al were investigated and it was determined that the out-gassing of moisture from siloxane SOG IMD significantly affects the via resistance and the key-hole formation in the via. A comparison of the via resistances of the Al-plug and W-plug was made. On the basis of the results, Al plugging with IMD materials such as HSQ or HDP oxide is considered to be superior to W plugging because of the lower via resistance and cost.

Synthesis of Low‐Dielectric Silica Aerogel Films by Ambient Drying

A new ambient drying process that is simple, effective, and reproducible has been developed to synthesize low‐k SiO2 aerogel thin films for intermetal dielectric (IMD) materials. The SiO2 aerogel films having a thickness of 9500 Å, a high porosity of 79.5%, and a low dielectric constant of 2.0 were obtained by a new ambient drying process using n‐heptane as a drying solvent.

Low dielectric fluorinated amorphous carbon thin films grown from C 6F 6 and Ar plasma

Fluorinated amorphous carbon (a-C:F) thin films were synthesized for applications in low dielectric constant intermetal dielectric materials. The deposition was carried out in a capacitively coupled, asymmetric plasma reactor using hexafluorobenzene (C 6F 6) as the source gas and argon as the carrier gas. The effects of applied rf power on the electric, optical and mechanical properties of the a-C:F films were investigated. The bonding structures and properties of the films were evaluated by FTIR spectrometry, UV-Vis spectrophotometry and stress measurements. The films exhibit a dielectric constant as low as 2.0 and have high transparency in the visible range. The deposition rate of the a-C:F films increases, reaches a maximum, and then gradually decreases with increasing rf power. High rf power raises the negative self-bias voltage at the substrate and leads to an increase in the content of conjugated CC bonds in the a-C:F films. As the negative self-bias voltage at the substrate is increased, the dielectric constant, residual stress, and graphitization of the a-C:F films are increased while the optical energy gap is decreased.