High Etch Resistance Research Articles

Effect of Metal Oxide Deposition on the Sensitivity and Resolution of E-Beam Photoresist.

Organic-inorganic hybrid resists offer a solution to the issue of low sensitivity in organic photoresists like poly(methyl methacrylate) (PMMA). In this study, an organic-inorganic hybrid resist (PMMA-Al2O3) with high sensitivity and resolution was prepared by depositing metal oxides into PMMA using sequential infiltration synthesis (SIS). PMMA-Al2O3 was prepared by precisely controlling the number of SIS cycles (<23) in various atomic layer deposition (ALD) processes to facilitate the growth of metal oxides within PMMA pores. The impact of different metal oxide contents and distributions on the sensitivity and resolution of electron beam exposure was investigated. Numerical simulations of the deposit formation within the PMMA pores were performed by solving the pore-scale ALD governing equations fed by the reactor-scale boundary conditions. The gradual pore constriction with SIS cycles was predicted and validated by the experimental charaterizations. The results demonstrated that PMMA-Al2O3 was prepared using 20 SIS cycles, which corresponds to the numerically predicted occurrence of the pore blockage at the upper region of the PMMA layer, exhibiting optimal electron beam (e-beam) resolution while enabling line exposure with a width of 50 nm. While the corresponding sensitivity was lower than those of the samples prepared using 5 and 10 SIS cycles, the degradation of the PMMA structure was affected under exposure. The pattern transfer results showed that the line width was well retained for 20 cycles of deposition because of the high etching resistance of Al2O3. This research is expected to provide an effective approach to developing next-generation high-performance photoresists.

Si-Containing Reverse-Gradient Block Copolymer for Inorganic Pattern Amplification in EUV Lithography.

Although extreme ultraviolet lithography (EUVL) has emerged as a leading technology for achieving high quality sub-10 nm patterns, the insufficient pattern height of photoresist patterns remains a challenge. Directed self-assembly (DSA) of block copolymers (BCPs) is expected to be a complementary technology for EUVL due to its ability to form periodic nanostructures. However, for a combination with EUV patterns, it is essential to develop advanced BCP systems that are suited to inorganic-containing EUV photoresists and offer improved resolution limits, pattern quality, and etch resistance. Here, we report a reverse-gradient BCP system, poly[(styrene-gradient-pentafluorostyrene)-b-4-tert-butyldimetilsiloxystyrene] [P(S-g-PFS)-b-P4BDSS] BCP, which enables universally vertically oriented lamellae even in the absence of a neutral layer, while also containing a Si-containing block with high etch resistance. The gradient block, characterized by a gradual compositional transition from the block junction to the tail, plays a crucial role in creating an adequate surface energy contrast that energetically drives the formation of perpendicular lamellae without neutral layer. When used as a pattern height enhancement layer in EUVL, a high aspect ratio (3.29) of patterns was achieved, thereby offering a supplementary solution for next-generation EUVL.

Low Temperature Wafer Bonding of Silicon Carbide/Aluminum Nitride

Because of the wide energy gap material properties and high compatibility with existing silicon material processing, silicon carbide (SiC) has become the preferred material for power management chips that have been used in electric vehicles. On the other hand, aluminum nitride (AlN) material has become the first choice for carrying wafers due to its high strain-resistant mechanical properties, strong dielectric coefficient, excellent thermal conductivity, and high etching resistance. In this study, the surface chemistry of silicon carbide was changed into an AlN-based material to perform wafer bonding processing to develop low-temperature bonding technology for silicon carbide/aluminum nitride materials. We found through experiments that it is quite difficult for a SiC wafer to bond with an AlN wafer even if the surfaces ofthe SiC wafer and the AlN wafer are subjected to conventional surface activation treatment using oxygen plasma or argon plasma. The possible reason is that although the surface of the SiC wafer is bombarded by oxygen or argon plasmas to generate some dangling bonds, the chemical properties of Si-C and Al-N, such as electronegativity, make it difficult to generate chemical bonds between the matching surfaces of SiC/AlN. Through a material modification technology, a high-temperature sputtering method is used to make highly active AlN clusters sputtered from the target directly bond with SiC and finally form a thin AlN layer that strongly adheres to the surface of the SiC wafer. And then through the bonding of AlN/AlN homogeneous materials, although the surface roughness measurement (RMS) cannot satisfy the condition of being less than 5 angstroms for wafer bonding, the goal of low-temperature bonding can be achieved by capillary bonding. Therefore, the SiC surface is changed into an AlN-based thin layer by high-temperature sputtering, which can further chemically bond with the AlN wafer surface by capillary bonding to achieve the low-temperature bonding of SiC/AlN, as shown in Figure 1.Reference1. Shao-Ming Nien, Jian-Long Ruan, Yang-Kuao Kuo, and Benjamin Tien-Hsi Lee, Low-temperature rough-surface wafer bonding with aluminum nitride ceramics implemented by capillary and oxidation actions, Ceramics International, Volume 48, Issue 6, 2022 Figure 1

Novel process integration flow of germanium-on-silicon FinFETs for low-power technologies

Germanium channel FinFET transistors process integration on a silicon substrate is a promising candidate to extend the complementary metal–oxide–semiconductor semiconductor roadmap. This process has utilized the legacy of state-of-art silicon fabrication process technology and can be an immediate solution to integrate beyond Si channel materials over standard Si wafers. The fabrication of such devices involves several complicated technological steps, such as strain-free epi layers over the Si substrate to limit the substrate leakage and patterning of narrow and sharp fins over germanium (Ge). To overcome these issues, the active p-type germanium layers were grown over n-type germanium and virtual substrates. The poly ((4-(methacryloyloxy) phenyl) dimethyl sulfoniumtriflate) was utilized as a polymeric negative tone e-beam resist for sub-20 nm critical dimensions with low line edge roughness, line width roughness, and high etch resistance to pattern p-Ge fins to meet these concerns. Here, the devices use the mesa architecture that will allow low bandgap materials only at the active regions and raised fins to reduce the active area interaction with the substrate to suppress leakage currents. This paper discusses the simple five-layer process flow to fabricate FinFET devices with critical optimizations like resist prerequisite optimization conditions before exposure, alignment of various layers by electron beam alignment, pattern transfer optimizations using reactive ion etching, and bilayer resist for desired lift-off. The Ge-on-Si FinFET devices are fabricated with a width and gate length of 15/90 nm, respectively. The devices exhibit the improved ION/IOFF in order of ∼105, transconductance Gm ∼86 μS/μm, and subthreshold slope close to ∼90 mV/dec.

Vapor‐Phase Infiltrated Organic–Inorganic Positive‐Tone Hybrid Photoresist for Extreme UV Lithography

AbstractContinuing extreme downscaling of semiconductor devices, essential for high performance and energy efficiency of future microelectronics, hinges on extreme ultraviolet lithography (EUVL) and addressing associated challenges. One of such challenges is a need for improved EUV photoresists featuring simultaneously high sensitivity, resolution, and etch selectivity. Here, a new, positive‐tone, organic–inorganic hybrid EUV photoresist is demonstrated that delivers a high‐resolution EUVL and electron‐beam lithography (EBL) patterning capability combined with high sensitivity and etch resistance. The new resist, poly(methyl methacrylate) infiltrated with indium oxide (PMMA‐InOx), is synthesized via vapor‐phase infiltration (VPI), a material hybridization technique derived from atomic layer deposition. The weak binding of the gaseous indium precursor, trimethylindium, to the carbonyl group in PMMA allows the synthesis of hybrids with inorganic content distributed uniformly in the resist, enabling high EUVL and EBL sensitivities (18 mJ cm−2 and 300 µC cm−2, respectively) and high‐resolution positive‐tone EUVL patterning (e.g., 40 nm half‐pitch line‐space and 50 nm diameter contact hole patterns) with high Si etch selectivity (&gt;30–40). The low exposure doses required to pattern the PMMA‐InOx hybrid resist, high etch resistance, and processing strategies, which are developed, can pave the way for using infiltration‐synthesized hybrid thin films as reliable positive‐tone EUV photoresists for future semiconductor patterning.

Chemical Mechanisms of Metal-Based Extreme Ultraviolet Resists

Hybrid organic/inorganic materials are considered as the Extreme Ultraviolet photoresists of the future. Compared to chemically amplified polymer-based photoresists they offer higher EUV absorption cross sections, and higher etch resistance. The chemical reactions that occur in these materials upon excitation with EUV or other high energy radiation have been investigated over the past 8 years. This paper summarizes the findings for two classes of metal-based resists: metal oxo clusters with acrylate ligands, and organotin oxo cages.

Molecular Layer Deposition of a Hafnium-Based Hybrid Thin Film as an Electron Beam Resist.

The development of new resist materials is vital to fabrication techniques for next-generation microelectronics. Inorganic resists are promising candidates because they have higher etch resistance, are more impervious to pattern collapse, and are more absorbing of extreme ultraviolet (EUV) radiation than organic resists. However, there is limited understanding about how they behave under irradiation. In this work, a Hf-based hybrid thin film resist, known as "hafnicone", is deposited from the vapor-phase via molecular layer deposition (MLD), and its electron-beam and deep-ultraviolet (DUV)-induced patterning mechanism is explored. The hafnicone thin films are deposited at 100 °C by using the Hf precursor tetrakis(dimethylamido)hafnium(IV) and the organic precursor ethylene glycol. E-beam lithography, scanning electron microscopy, and profilometry are used to investigate the resist performance of hafnicone. With 3 M HCl as the developer, hafnicone behaves as a negative tone resist which exhibits a sensitivity of 400 μC/cm2 and the ability to resolve 50 nm line widths. The resist is characterized via X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR) to investigate the patterning mechanism, which is described in the context of classical nucleation theory. This study of hafnicone hybrid MLD demonstrates the ability for the bottom-up vapor deposition of inorganic resists to be utilized in advanced e-beam and DUV lithographic techniques.

Remarkable plasma-resistance performance by nanocrystalline Y2O3\xb7MgO composite ceramics for semiconductor industry applications

Motivated by recent finding of crystallographic-orientation-dependent etching behavior of sintered ceramics, the plasma resistance of nanocrystalline Y2O3-MgO composite ceramics (YM) was evaluated for the first time. We report a remarkably high plasma etching resistance of nanostructure YM surpassing the plasma resistance of commercially used transparent Y2O3 and MgAl2O4 ceramics. The pore-free YM ceramic with grain sizes of several hundred nm was fabricated by hot press sintering, enabling theoretical maximum densification at low temperature. The insoluble two components effectively suppressed the grain growth by mutual pinning. The engineering implication of the developed YM nanocomposite imparts enhanced mechanical reliability, better cost effectiveness with excellent plasma resistance property over their counterparts in plasma using semiconductor applications.

Plasma-Enhanced Atomic-Layer Deposition of Nanometer-Thick SiNx Films Using Trichlorodisilane for Etch-Resistant Coatings

In recent times, the requirements have become extremely stringent for employing silicon nitride (SiNx) films in various types of applications. For instance, high etch resistance coating is required...

Medusa 82—Hydrogen silsesquioxane based high sensitivity negative-tone resist with long shelf-life and grayscale lithography capability

The high suitability of hydrogen silsesquioxane (HSQ) as e-beam resist has long been known. Despite its undoubtedly good and reliable properties, HSQ nevertheless proves to be problematic in certain aspects due to its relatively short shelf-life and the small processing window between coating preparation and exposure. We thus intended to optimize the silsesquioxane with respect to a prolonged shelf-life and larger processing window while retaining all advantages like the high silicon content for high etch resistance and high pattern resolution. Our combined knowledge resulted in the development of the hydrogen silsesquioxane-based e-beam resist Medusa 82 with improved characteristics. Medusa 82 can be processed with HSQ standard procedures but allows for a delay of several weeks between layer preparation and exposure under standard conditions. Medusa 82 resist compositions tolerate storage periods of several weeks at room temperature. In addition, we generated and investigated variants of Medusa 82, which offer the possibility for exposure with less energy to cross-link the resist. Furthermore, weaker alkaline developers can be applied. A postexposure bake of these new Medusa 82 variants provides a significant enhancement of sensitivity and contrast. In this context, applications of Medusa 82 in deep to extreme ultraviolet and grayscale lithography are described. The use of glasslike resists with moderate electron beam sensitivity has the potential to reduce the effort and to simplify the manufacturing process of micro-optical devices that traditionally have to be structured in glass surfaces. The transformation process of Medusa 82 into a glasslike material involves an e-beam exposure, a thermal treatment, or a combination of both. Moreover, the adjustable contrast and sensitivity enable grayscale lithography. Different e-beam exposures trigger a different cross-linking degree within the layer, resulting in height variations after development. A postexposure bake step induces further cross-linking and a complete conversion into silicon oxide.

Process study and the lithographic performance of commercially available silsesquioxane based electron sensitive resist Medusa 82

Abstract In the past 2 decades silsesquioxane has gained attention in the Electron Beam Lithography community as a negative tone electron-sensitive resist (HSQ) whose advantages (sub-20 nm resolution, high contrast, low Line Edge Roughness, good shape fidelity and high etch resistance) outnumber its associated drawbacks (limited shelf-life, chemical instability issues, process residuals, low sensitivity, cost). The new silsesquioxane based resist, developed by Allresist GmbH, Medusa 82 (official product name: SX AR-N 8200) and Medusa 82 UV (SX AR-N 8250), its highly sensitive counterpart, have been designed to address all these issues. The objective of this work is to use fundamental Contrast Curve analysis, Dissolution Monitoring and parametric e-beam lithography experiments to study the influence of processing conditions (Post Exposure Bake Temperature, Development duration and developer strength) on the lithographic performance of sub-40 nm thick films.

Graphene-Based Etch Resist for Semiconductor Device Fabrication

As the feature size of semiconductor devices decreases, the resist layer with high etch resistance is required to achieve fine pattern transfer during lithography. Conventional resists (e.g., amorp...

High growth rate and high wet etch resistance silicon nitride grown by low temperature plasma enhanced atomic layer deposition with a novel silylamine precursor

Trisilylamine homolog, tris(disilanyl)amine (TDSA), is introduced as a novel precursor for the deposition of highly etch resistant silicon nitride thin films having a high growth rate at a low temperature (&lt;300 °C) using plasma enhanced ALD process.

Overlay error investigation for metal containing resist

Metal containing resists (MCR) are one of the candidates for extreme ultraviolet resists aiming to achieve the resolution, linewidth roughness, and sensitivity requirements of advanced design nodes. MCRs intrinsically have high etch resistance owing to their metal content. Therefore, low resist thickness (∼18 nm) is sufficient to transfer resist patterns into an underlying hard mask. Also, the thin resist reduces susceptibility to pattern collapse during development because of low aspect ratio. However, thus far, little attention has been paid to optical metrology and inspectability (overlay, defect inspection, scatterometry, etc.) of these resists, which is another critical requirement to move MCR toward high-volume manufacturing. We investigate the overlay metrology and overlay correction with MCR. Even though the optical contrast for MCR is slightly lower than for chemically amplified resist (CAR), it seemed sufficient for high-quality overlay metrology. However, the measurement precision for MCR is deteriorated compared to that for CAR, resulting in significantly higher residuals. The root cause of the deteriorated measurement precision was found in grains in the optical image after MCR development. Interestingly, the after etch performance of CAR and MCR is identical. We demonstrate that with sufficient sampling, appropriate correctables can be extracted from the MCR overlay results. Finally, we discuss how the increased image noise can be compensated by the applied sampling scheme.

Plasma-Etched Pattern Transfer of Sub-10 nm Structures Using a Metal-Organic Resist and Helium Ion Beam Lithography.

Field-emission devices are promising candidates to replace silicon fin field-effect transistors as next-generation nanoelectronic components. For these devices to be adopted, nanoscale field emitters with nanoscale gaps between them need to be fabricated, requiring the transfer of, for example, sub-10 nm patterns with a sub-20 nm pitch to substrates like silicon and tungsten. New resist materials must therefore be developed that exhibit the properties of sub-10 nm resolution and high dry etch resistance. A negative tone, metal-organic resist is presented here. It can be patterned to produce sub-10 nm features when exposed to helium ion beam lithography at line doses on the order of tens of picocoulombs per centimeter. The resist was used to create 5 nm wide, continuous, discrete lines spaced on a 16 nm pitch in silicon and 6 nm wide lines on an 18 nm pitch in tungsten, with line edge roughness of 3 nm. After the lithographic exposure, the resist demonstrates high resistance to silicon and tungsten dry etch conditions (SF6 and C4F8 plasma), allowing the pattern to be transferred to the underlying substrates. The resist's etch selectivity for silicon and tungsten was measured to be 6.2:1 and 5.6:1, respectively; this allowed 3 to 4 nm thick resist films to yield structures that were 21 and 19 nm tall, respectively, while both maintained a sub-10 nm width on a sub-20 nm pitch.

Reaction mechanisms between chlorine plasma and a spin-on-type polymer mask for high-temperature plasma etching

To satisfy the requirement for mask materials in high-temperature plasma etching, a novolac-based polymer mask was evaluated during high-temperature Cl2 plasma etching. Although the etch rate of 8 nm/min was rather high at a low temperature of 230 °C, it decreased with the increase in temperature. The aromatic ring structures were significantly modified by vacuum ultraviolet (VUV) and Cl radicals during the processes above 300 °C and transformed to a highly cross-linked amorphous carbon (a-C) layer at the surface confirmed from infrared and Raman spectra. The formation of this a-C layer improved the etching resistance of the polymer mask. On the other hand, surface roughness can also be improved after processes above 300 °C corresponding to the generation of the a-C layer. Therefore, this polymer mask is a promising candidate for high-temperature plasma etching with high etch resistance, and a smooth surface can be obtained during processes above 300 °C.

Remote plasma atomic layer deposition of silicon nitride with bis(dimethylaminomethyl-silyl)trimethylsilyl amine and N2 plasma for gate spacer

The silicon nitride (SiNx) atomic layer deposition with bis(dimethylaminomethylsilyl)-trimethylsilyl amine precursor and N2 remote plasma was investigated. The process window ranged from 250 to 400 °C, and the growth rate was about 0.38 ± 0.02 Å/cycle. The physical, chemical, and electrical characteristics of the SiNx thin films were examined as a function of deposition temperature and plasma power. Based on the results of spectroscopic ellipsometry and x-ray photoelectron spectroscopy, the growth rate and state of binding energy showed little difference depending on the plasma power. The better film properties such as leakage current density and etch resistance were obtained at higher deposition temperatures and higher plasma power. High wet etch resistance (wet etch rate of ∼2 nm/min) and low leakage current density (∼10−8 A/cm2) were obtained. The step coverage, examined by transmission electron microscopy, was about 80% on a trench with an aspect ratio of 4.5.

Lithographic performance of ZEP520A and mr-PosEBR resists exposed by electron beam and extreme ultraviolet lithography

Pattern transfer by deep anisotropic etch is a well-established technique for fabrication of nanoscale devices and structures. For this technique to be effective, the resist material plays a key role and must have a high resolution, reasonable sensitivity, and high etch selectivity against the conventional silicon substrate or underlayer film. In this work, the lithographic performance of two high etch resistance materials was evaluated: ZEP520A (Nippon Zeon Co.) and mr-PosEBR (micro resist technology GmbH). Both materials are positive tone, polymer-based, and nonchemically amplified resists. Two exposure techniques were used: electron beam lithography (EBL) and extreme ultraviolet (EUV) lithography. These resists were originally designed for EBL patterning, where high quality patterning at sub-100 nm resolution was previously demonstrated. In the scope of this work, the authors also aim to validate their extendibility to EUV for high resolution and large area patterning. For this purpose, the same EBL process conditions were employed at EUV. The figures of merit, i.e., dose to clear, dose to size, and resolution, were obtained, and these results are discussed systematically. It was found that both materials are very fast at EUV (dose to clear lower than 12 mJ/cm2) and are capable of resolving dense lines/space arrays with a resolution of 25 nm half-pitch. The quality of patterns was also very good, and the sidewall roughness was below 6 nm. Interestingly, the general-purpose process used for EBL can be extended straightforwardly to EUV lithography with comparably high quality and yield. Our findings open new possibilities for lithographers who wish to devise novel fabrication schemes exploiting EUV for fabrication of nanostructures by deep etch pattern transfer.

Characterization of Ammonium Silicate Residue during Polysilazane (PSZ) Dry Etching in NF3/ H2O Gas Chemistry

For 28nm NAND flash memory, the aspect ratio of shallow trench isolation (STI) becomes large, and it makes difficult to fill STI structure by conventional oxide film without void formation. Several gap-fill methods such as high density plasma (HDP) and thermal chemical vapor deposition (CVD) are widely accepted, but they are difficult to make gap fill without void because of gap-fill margin. Recently, STI fill has been tried with polysilazane (PSZ) based inorganic spin-on dielectric (SOD) film. PSZ oxide has its good gap-fill ability, low moisture content and high etching resistance. However, PSZ oxide would produce amine etch residue during the NF3 dry etching process because of NH3component in PSZ oxide. For preventing this resudue, it is very important to control process parameters affecting the chemical reaction because the etch rate, and the surface quality depend upon the process reaction. During the STI etching back process, other layer also exposed. So, selectivity between other oxide must be considered. In this study, we have employed plasma dry etching of nitrogen trifluoride (NF3) and H2O mixtures. We studied the effect of the gas chemistry on the etching of oxides. The materials used for these experiments were thermally grown SiO2 (1000Å, 10000Å), PSZ oxide (500Å), TEOS (315Å) and ALD oxide (300Å). Samples of size 25 x 25 mm were cleaned first in diluted SC-1 [NH4OH(25%): H2O2(38%): DIW =1:2:50] at 60°C for 10 min. The etching mechanism of PSZ oxide was investigated in plasma activated NF3/H2O gas. This process generates ammonium hexafluorosilicate ((NH4)2SiF6) as a by-product. By-products were formed on the PSZ surface which was confirmed by observing N–H, NH4+ and SiF6 2-peak in ATR-FTIR spectrum. These peaks are representative of (NH4)2SiF6 powder composition. Etch rates of several SiO2 were reported as a function of H2O ratio, substrate temperature, and pressure. NF3/H2O mixtures were excited using pulsed RF plasma. The NF3 flow rate for all experiments was kept at 150 sccm. The temperatures were varied from 8 to18ºC, the chamber pressures from 7 to 9 Torr., the H2O flow rates from 1500 to 2500 sccm and process times from 20 to 100 sec. Helium was used as a carrier gas. After dry etching, an annealing process was performed. The reaction mechanism was proposed by analyzing the oxide layer surface. We used an ellipsometer to measure the oxide thickness for evaluation of the etch rate. Also, various analyzing tools such as SEM, contact angle analyzer, and FT-IR were used to characterize the surface contaminants. The optimized drying process provides the high selectivity without any residue formation.

Ion Etching Induced Surface Patterns of Blend Polymer (Poly Ethylene Glycol – Poly Methyl Methacrylate) Irradiated with Gamma Rays

Abstract The pattern surface structure of a thin blend polymer film of Poly methyl methacrylate (PMMA) – Poly ethylene glycol (PEG) induced by Ar+ ion etching (5 keV) has been investigated by scanning electron microscopy. Blend polymer films have been obtained consisting of a hydrophilic PEG and a hydrophobic PMMA distributed in co-continuous phases. Four different compositions of the two polymers are dissolved in chloroform and irradiated with gamma rays (60Co) at 20 kGy to produce transparent films of blend polymer PMMA-PEG after casting. Self-assembled of PMMA-PEG film is obtained because of the high contrast between the two polymers. Ion-polymer interaction with a hydrophilic polymer (Ar+ +PEG) rather than the high etch resistance of hydrophobic polymer (Ar+ −PMMA) was observed. The results are discussed in terms of significant destruction of bonds in the blend polymer films as a result of which one polymer undergoes rapid dissociation rather than the other one. This means that etching with Ar+ ions of the PMMA domains are stable and PEG can be selective. The ATR-FTIR spectrum shows the absence of hydrogen bonds and XRD/DSC curves show the crystanility of PMMA depending on the PEG contents and gamma radiation effect, irradiated blend polymer PMMA/PEG has shown more resistant at thermal degradation than irradiated PMMA. This indicates that the PEG contents have an effect on the thermal stability of PMMA/PEG as detected by TGA. Finally, the pattern surface of irradiated blend polymer (PMMA-2%PEG) was plated with two coaxial layers subsequently of copper (Cu) and silver (Ag) using sputter technique.