Fullerene Resist Materials for the 32 nm Node and Beyond

Current resist materials cannot simultaneously meet the sensitivity, resolution and line width roughness (LWR) requirements set out by the International Technology Roadmap for Semiconductors (ITRS) for the 32nm node and beyond. Here we present a fullerene‐based, chemically amplified resist system, which demonstrates the potential to fulfill these requirements for next generation lithography. A chemically amplified fullerene resist was prepared, consisting of the derivative MF07‐01, an epoxide crosslinker, and a photoacid generator, such as triarylsulfonium hexafluoroantimonate. The sensitivity of this resist was shown to be between 5 and 10 µC cm^?2 at 20 keV for various combinations of post‐application bake and post‐exposure bake conditions. Using 30 keV electron beam exposure, sparse patterns with 15 nm resolution were demonstrated, whilst for dense patterns a half‐pitch of 25 nm could be achieved. The LWR for the densely patterned features is ～4 nm. The etch durability of the fullerene CA system was shown to be comparable to that of SAL601, a common novolac‐based commercial resist, at almost four times that of silicon.     

Anomalous acid diffusion in a triphenylene molecular resist with melamine crosslinker

Next generation lithography will require next generation resists. Molecular resists, based on small non-polymeric molecules, promise improvements in line width roughness and resolution control for high resolution lithographic patterns. However, these materials are generally not sensitive enough for commercial application. We have investigated the application of a common chemical amplification scheme to molecular resists. The triphenylene derivative C5/C0 (symmetrical 2,6,11-trihydroxy-3,7,11-tris(pentyloxy)triphenylene), mixed with the crosslinker hexamethoxymethyl melamine and the photoacid generator triphenylsulfonium triflate shows a substantial sensitivity enhancement, requiring a dose of only 5 μC/cm² compared with the pure triphenylene sensitivity of 6500 μC/cm² at 20 keV. Previous work has indicated that the acid diffusion length of the photoacid generator used here is around 350 nm and that the diffusion length decreases with film thickness. However, in this molecular resist system anomalous levels of acid diffusion were observed, indicating that previous results for polymeric systems may not hold true for these new materials. Initial results indicate that the acid diffusion length in this system may be on the order of microns. Furthermore, there is some evidence that the excessive diffusion is occurring in the surface layers of the resist or at the air: resist interface itself.     

Formation and study of buried SiC layers with a high content of radiation defects

Protons with energy E=100 keV were implanted with doses ranging from 2×10¹⁷ to 4×10¹⁷ cm^?2 into 6H-and 4H-SiC n-type samples at room temperature. The samples were subjected to various types of postimplantation heat treatment in the temperature range 550–1500°C. The parameters of the samples were studied by measuring the capacitance-voltage and current-voltage characteristics and by analyzing the photoluminescence spectra. Blistering on the surface of the sample is observed after annealing the samples at a temperature of 800°C only after implantation of protons with a dose of ≤3×10¹⁷ cm^?2. A decrease in the resistivity of the compensated layer sets in after annealing at a temperature of ～1200°C and is completed after annealing at a temperature of ～1500°C. A drastic decrease in the photoluminescence intensity is observed after implantation for all types of samples. Recovery of the photoluminescence intensity sets in after annealing at temperatures ≥800°C and is complete after annealing at a temperature of 1500°C.     

Some annealing properties of low-energy-antimony—implanted silicon resistors

Shallow-implanted antimony in silicon can be used in fabricating n-type silicon resistors with very low temperature coefficient of resistance (TCR), controllably and reproducibly. This paper reports a study of the sheet resistance of silicon resistors implanted with ¹²¹Sb at 10 keV, for various doses and annealing conditions. The methods used in fabricating samples and taking measurements were described in an earlier paper[1]. For high doses, ～ 10¹⁵ Sb/cm², we found that two-stage annealing[2]—preannealing at 550°C followed by annealing at 1000°C—improves the electrical conductivity. For low doses, ～10¹² Sb/cm², the final annealing determines the conductivity. For medium doses, ～10¹³–10¹⁴ Sb/cm², the interplay of damage-annealing and activation of Sb in Si introduces complications, giving a crossover of shet resistance vs implant dose for various annealing temperatures. For doses around 3 × 10¹³ cm^?2, the resistances are very insensitive to the details of annealing sequence and temperature; also the TCR is very low, about 50 ppm/°C. The effect of annealing conditions for various doses, resistivities and TCR values are discussed.     

UV-photoassisted etching of GaN in KOH

The etch rate of GaN under ultraviolet-assisted photoelectrochemical conditions in KOH solutions is found to be a strong function of illumination intensity, solution molarity, sample bias, and material doping level. At low e-h pair generation rates, grain boundaries are selectively etched, while at higher illumination intensities etch rates for unintentionally doped (n～ 3×10¹⁶cm^?3) GaN are ≥1000Å·min^?1. The etching is diffusion-limited under our conditions with an activation energy of ～ 0.8kCal·mol^?1. The etched surfaces are rough, but retain their stoichiometry.     

Carrier Lifetimes of Iodine-Doped CdMgTe/CdSeTe Double Heterostructures Grown by Molecular Beam Epitaxy

Iodine-doped CdMgTe/CdSeTe double heterostructures (DHs) have been grown by molecular beam epitaxy and studied using time-resolved photoluminescence (PL), focusing on absorber layer thickness of 2 μm. The n-type free carrier concentration was varied to ～7 × 10¹⁵ cm^?3, 8.4 × 10¹⁶ cm^?3, and 8.4 × 10¹⁷ cm^?3 using iodine as dopant in DHs. Optical injection at 1 × 10¹⁰ photons/pulse/cm² to 3 × 10¹¹ photons/pulse/cm², corresponding to initial injection of photocarriers up to ～8 × 10¹⁵ cm^?3, was applied to examine the effects of excess carrier concentration on the PL lifetimes. Iodine-doped DHs exhibited an initial rapid decay followed by a slower decay at free carrier concentration of 7 × 10¹⁵ cm^?3 and 8.4 × 10¹⁶ cm^?3. The optical injection dependence of the carrier lifetimes for DHs was interpreted based on the Shockley–Read–Hall model. The observed decrease in lifetime with increasing n is consistent with growing importance of radiative recombination.     

High purity and chrome-doped GaAs buffer layers grown by liquid phase epitaxy for mesfet application

High purity GaAs buffer layers of carrier concentration in the low (l-5)×l0^l4/cm³ range with 77K electron mobility over 100,000 cm²/V-sec and 300K mobility around 8000 cm?/ V-sec have been grown by liquid phase epitaxy on Cr-doped GaAs substrates using the graphite sliding boat method. The high purity has been achieved with systematic and concurrent long term bake-outs (24 hrs) of both LPE melt and substrate, both exposed to the H₂ ambient gas stream at 775?C, prior to epitaxial growth at 700?C. Substrate surface degradation was reduced by using Ga:GaAs etch melts that were undersaturated at 700?C by 5? to 40?C. Best buffer layer morphologies with regard to surface planarity were obtained using etch melts that were saturated by near 85% of weight of GaAs at 700°C. The importance of substrate preconditioning in order to achieve the low ( 1 -2)×l0¹⁴ was examined and found to be critical. Melt and substrate bake outs at 800?C, and use of a 40?C undersaturated etch melt prior to epitaxial growth at 800?C resulted in a p-type layer of carrier concentration, 1 .9×l0^l2/cm³ and resistivity 1×10⁵ ohm-cm. Chromium doping at 700?C resulted in buffer layers with sheet resistivities greater than 10 ohms/sq and low pinhole densities.     

Halogen lamp rapid thermal annealing of Si- and Be-implanted In0.53Ga0.47As

Halogen lamp rapid thermal annealing was used to activate 100 keV Si and 50 keV Be implants in In_0.53Ga_0.47As for doses ranging between 5 × 10¹²−4 × 10¹⁴ cm⁻². Anneals were performed at different temperatures and time durations. Close to one hundred percent activation was obtained for the 4.1 × 10¹³ cm⁻² Si-implant, using an 850° C/5 s anneal. Si in-diffusion was not observed for the rapid thermal annealing temperatures and times used in this study. For the 5 × 10¹³ cm⁻² Be-implant, a maximum activation of 56% was measured. Be-implant depth profiles matched closely with gaussian profiles predicted by LSS theory for the 800° C/5 s anneals. Peak carrier concentrations of 1.7 × 10¹⁹ and 4 × 10¹⁸ cm⁻³ were achieved for the 4 × 10¹⁴ cm⁻² Si and Be implants, respectively. For comparison, furnace anneals were also performed for all doses.     

The accumulation of radiation defects in gallium arsenide that has been subjected to pulsed and continuous ion implantation

Measurements of electrical conductivity and Rutherford backscattering are used to study the accumulation of defects in GaAs that has been subjected to pulsed (τ_p = 1.3 × 10^?2 s and an off-duty factor of 100) and continuous irradiation with ³²S, ¹²C, and ⁴He ions at room temperature at the ion energies E=100–150 keV, doses Φ = 1 × 10⁹–6 × 10¹⁶ cm^?2, and current densities j = 1 × 10^?9–3 × 10^?6 A cm^?2. It is shown that the defect-accumulation rate during the pulsed implantation is much lower than it is during the continuous implantation.     

Controlled gallium diffusion in silicon by an open-tube system

A novel method of open-tube diffusion of gallium in silicon is explored in this work. A two-temperature zone furnace is used to chemically transport a solid gallium trioxide diffusion source under quasi-equilibrium conditions. By accurately controlling the composition of the input gases, it has been possible to obtain highly reproducible gallium diffusion profiles with ～5 × 10¹⁵–～10¹⁹cm^?3 surface concentrations and 1 to ～50 μm junction depths with resultant sheet resistivities of $\text{～10 to 5 × 10}{}^4\text{Ω/□}$. A compatible masking system for selective area diffusion was also successfully developed. An analysis of the present data concluded that the active diffusing species in this system is elemental gallium. The determined gallium diffusivities agreed closely with the comparable literature data.     

Dislocation-related luminescence in single-crystal silicon subjected to silicon ion implantation and subsequent annealing

Implantation of silicon ions with an energy of 100 keV at a dose of 1 × 10¹⁷ cm^?2 into n-type floatzone Si does not lead to the formation of an amorphous layer. Subsequent annealing in a chlorine-containing atmosphere at 1100°C gives rise to dislocation-related luminescence. The intensity of the dominant D1 line peaked at a wavelength of ～1.54 μm grows as the annealing time is increased from 15 to 60 min.     

Electrical properties of Si:H/<Emphasis Type="Italic">p</Emphasis>-Si structures fabricated by hydrogen implantation

Hydrogenated silicon (Si:H) layers and Si:H/p-Si heterostructures were produced by multiple-energy (3–24 keV) high-dose (5×10¹⁶–3×10¹⁷ cm^?2) hydrogen implantation into p-Si wafers. After implantation, current transport across the structures is controlled by the Poole-Frenkel mechanism, with the energy of the dominating emission center equal to E _c ?0.89 eV. The maximum photosensitivity is observed for structures implanted with 3.2×10¹⁷ cm^?2 of hydrogen and annealed in the temperature range of 250–300°C. The band gap of the Si:H layer E _g ≈2.4 eV, and the dielectric constant ?≈3.2. The density of states near the Fermi level is (1–2)×10¹⁷ cm^?3 eV^?1.     

Rapid thermal annealing of si implanted gaas

Rapid thermal annealing (RTA) technology offers potential advantages for GaAs MESFET device technology such as reducing dopant diffusion and minimizing the redistribution of background impurities. LEC semi-insulating GaAs substrates were implanted with Si at energies from 100 to 400 keV to doses from 1 × 10¹² to 1 × 10¹⁴/cm². The wafers were encapsulated with Si₃N₄ and then annealed at temperatures from 850-1000° C in a commercial RTA system. Wafers were also annealed using a conventional furnace cycle at 850° C to provide a comparison with the RTA wafers. These implanted layers were evaluated using capacitance-voltage and Hall effect measurements. In addition, FET’s were fabricated using selective implants that were annealed with either RTA or furnace cycles. The effects of anneal temperature and anneal time were determined. For a dose of 4 × 10¹²/cm² at 150 keV with anneal times of 5 seconds at 850, 900, 950 and 1000° C the activation steadily increased in the peak of the implant with overlapping profiles in the tail of the profiles, showing that no significant diffusion occurs. In addition, the same activation could be obtained by adjusting the anneal times. A plot of the equivalent anneal times versus 1/T gives an activation energy of 2.3 eV. At a higher dose of 3 × 10¹³ an activation energy of 1.7 eV was obtained. For a dose of 4 × 10¹² at 150 keV both the RTA and furnace annealing give similar activations with mobilities between 4700 and 5000 cm²/V-s. Mobilities decrease to 4000 at a dose of 1 × 10¹³ and to 2500 cm²/V-s at 1 × 10¹⁴/cm². At doses above 1 × 10¹³ the RTA cycles gave better activation than furnace annealed wafers. The MESFET parameters for both RTA and furnace annealed wafers were nearly identical. The average gain and noise figure at 8 GHz were 7.5 and 2.0, respectively, for packaged die from either RTA or furnace annealed materials.     

The effect of dose rate and implant temperature on transient enhanced diffusion in boron implanted silicon

The effect of ion implantation dose rate and implant temperature on the transient enhanced diffusion (TED) of low energy boron implants into silicon was investigated. The implant temperature was varied between 5 and 40°C. The beam current was varied from 0.035 to 0.35 mA/cm². Three different defect regimes were investigated. The first regime was below the formation of any extended defects (5 keV B⁺ 2 × 10¹⁴/cm²) visible in the transmission electron microscope. The second regime was above the {311} formation threshold (2×10¹⁴/cm²) but below the subthreshold (type I) dislocation loop formation threshold. The final regime was above both the {311} and dislocation loop formation threshold (10 keV 5×10¹⁴/cm²). TED for these conditions is shown to be over after annealing at 750°C for 15–30 min. Secondary ion mass spectroscopy results for the three different damage regimes indicate that there is no measurable effect of dose rate or implant temperature on TED of boron implanted silicon for any of the damage regimes. It should be emphasized that the dose and energy of the boron implants is such that none of these implants approached the amorphization threshold. Above amorphization dose rate and implant temperature have dramatic effects on TED, but it appears that below the amorphization threshold there is little effect. These results suggest that for a given energy it is the ion dose not the extent of the implant damage that determines the extent of TED in boron implanted silicon.     

Zinc-Imidazolate Films as an All-Dry Resist Technology

Motivated by the drawbacks of solution phase processing, an all-dry resist formation process is presented that utilizes amorphous zinc-imidazolate (aZnMIm) films deposited by atomic/molecular layer deposition (ALD/MLD), patterned with electron beam lithography (EBL), and developed by novel low temperature (120 °C) gas phase etching using 1,1,1,5,5,5-hexafluoroacetylacetone (hfacH) to achieve well-resolved 22 nm lines with a pitch of 30 nm. The effects of electron beam irradiation on the chemical structure and hfacH etch resistance of aZnMIm films are investigated, and it is found that electron irradiation degrades the 2-methylimidazolate ligands and transforms aZnMIm into a more dense material that is resistant to etching by hfacH and has a C:N:Zn ratio effectively identical to that of unmodified aZnMIm. These findings showcase the potential for aZnMIm films to function in a dry resist technology. Sensitivity, contrast, and critical dimensions of the patterns are determined to be 37 mC cm⁻², 0.87, and 29 nm, respectively, for aZnMIm deposited on silicon substrates and patterned at 30 keV. This work introduces a new direction for solvent-free resist processing, offering the prospect of scalable, high-resolution patterning techniques for advanced semiconductor fabrication processes.     

Amorphization and Solid-Phase Epitaxial Growth of C-Cluster Ion-Implanted Si

Amorphization and solid-phase epitaxial growth were studied in C-cluster ion-implanted Si. C₇H₇ ions were implanted at a C-equivalent energy of 10 keV to C doses of 0.1 × 10¹⁵ cm⁻² to 8.0 × 10¹⁵ cm⁻² into (001) Si wafers. Transmission electron microscopy revealed a C amorphizing dose of ~5.0 ×  10¹⁴ cm⁻². Annealing of amorphized specimens to effect solid-phase epitaxial growth resulted in defect-free growth for C doses of 0.5 × 10¹⁵ cm⁻² to 1.0 × 10¹⁵ cm⁻². At higher doses, growth was defective and eventually polycrystalline due to induced in-plane tensile stress from substitutional C incorporation.     

Polymers as masks for Ion implantation

Polymers such as polyimides and photoresists, commonly used in semiconductor processing, have been investigated as high resolution masks for ion implantation. Thin films consisting of these materials were subjected to various implant doses of H⁺, Ne⁺ and Ar⁺ ions and the post implantation surface morphologies investigated. Polyimides maintained their integrity under severe H⁺ and Ne⁺ implant doses as high as 2.4 × 10¹⁶ cm⁻² and 1.0 × 10¹⁶ cm⁻², respectively, whereas photoresists began to degrade at implant doses of 9.6 × 10¹⁵ cm⁻² and 1.9 × 10¹⁵ cm⁻², respectively. When polyimide was H⁺ implanted with doses up to 10¹⁶ cm⁻² its dielectric constant and breakdown strength remained unchanged at 3.5 and 150 V/μm, respectively. However, a gradual increase in the dielectric constant was observed for doses above this level. It was also observed that under the influence of H⁺ implants with beam current densities exceeding 10⁻⁷ A-cm⁻² a hardening of the polyimide occurs, resulting in reduction of the etching rate in an O₂ plasma. The stopping powers of various polymers for H⁺ implants have been measured. The results show that the experimental energy loss rate for protons in these materials lies between 75–100 keV/μm.     

Low-temperature growth of silicon epitaxial layers codoped with erbium and oxygen atoms

The fabrication technology and properties of light-emitting Si structures codoped with erbium and oxygen are reported. The layers are deposited onto (100) Si by molecular beam epitaxy (MBE) using an Er-doped silicon sublimation source. The partial pressure of the oxygen-containing gases in the growth chamber of the MBE facility before layer growth is lower than 5 × 10^?10 Torr. The oxygen and erbium concentrations in the Si layers grown at 450°C is ～1 × 10¹⁹ and 10¹⁸ cm^?3, respectively. The silicon epitaxial layers codoped with erbium and oxygen have high crystal quality and yield effective photoluminescence and electroluminescence signals with the dominant optically active Er-1 center forming upon postgrowth annealing at a temperature of 800°C.     

Effect of annealing temperature on 1.5 μm photoluminescence from Er-lmplanted 6H-SiC

The effect of post-implantation anneal on erbium-doped 6H-SiC has been investigated. 6H-SiC has been implanted with 330 keV Er⁺ at a dose of 1 × 1013 /cm2. Er depth profiles were obtained by secondary ion mass spectrometry (SIMS). The as-implanted Er-profile had a peak concentration of∼1.3 × 10¹⁸/cm³ at a depth of 770Å. The samples were annealed in Ar at temperatures from 1200 to 1900°C. The photoluminescence intensity integrated over the 1.5 to 1.6 μm region is essentially independent of annealing temperature from 1400 to 1900°C. Reduced, but still significant PL intensity, was measured from the sample annealed at 1200°C. The approximate diffusivity of Er in 6H SiC was calculated from the SIMS profiles, yielding values from 4.5 × 10⁻¹⁶ cm²/s at 1200°C to 5.5 × 10⁻¹⁵ cm²/s at 1900°C.     

Large,Switchable Electrochromism in the Visible Through Far‐Infrared in Conducting Polymer Devices

Advanced materials with large and dynamic variation in thermal properties, sought for urgent defense and space applications, have heretofore been elusive. Conducting polymers (CPs) have shown some intrinsic variation of mid‐ to far‐infrared (IR) signature in this respect, but the practical utilization of this has remained elusive. We report herein the first significant IR electrochromism in any material, to our knowledge, in the 0.4 through 45 μm region. This is seen in practical CP devices in the form of thin (<0.5 mm), flexible, entirely solid‐state, variable area (1 cm² to 1 m²) flat panels. Typical properties include: very high reflectance variation; switching times <2 s; cyclabilities of 10⁵ cycles; emittance variation from 0.32 to 0.79; solar absorptance variation from 0.39 to 0.79; operating temperatures of –35 to +85 °C; durability against γ‐radiation to 7.6 Mrad, vacuum to 10^–6 torr, and simulated solar wind (e.g., 6.5 × 10¹⁶ e/cm² @ 10 keV).