High Aspect Ratio Patterns Research Articles

High-temperature atomic layer deposition of silicon oxide films using Tris(dimethylamino)silane and ozone

Atomic layer deposition (ALD) benefits from high process temperatures when the substrate is not temperature-sensitive because the films deposited at higher temperatures exhibit better electrical properties. In this study, we investigated the ALD process of silicon oxide films by alternating injections of tris(dimethylamino)silane (tris-DMAS) and O3/O2 at temperatures ranging from 400 to 700 °C. The saturation dose of tris-DMAS was 1.5 × 106 L at 400 °C. Self-limiting growth with a growth rate of approximately 0.9 Å/cycle was observed up to 600 °C, allowing excellent step coverage. However, at 700 °C, the growth rate increased significantly to 4.6 Å/cycle, carbon and nitrogen impurities were detected by secondary ion mass spectrometry, and step coverage was poor, supporting the thermal decomposition of tris-DMAS at this temperature. Therefore, the optimum temperature for ALD SiO2 using tris-DMAS is 600 °C for application as an insulating film on high aspect ratio patterns. At this temperature, the leakage current density was 0.58 nA/cm2, and the oxide-trapped charge density was 4.0 × 1010 cm−2.

Efficiency of high energy fluorocarbon molecule bombardment for fast etch rate and its limitation: A molecular dynamics study

The RF power of the High Aspect Ratio (HAR) patterning equipment used for 3D NAND memory etching processes rapidly increased recently. However, despite implementing higher ion energy, its effect on increasing the etch rate is not satisfactory. This letter studies the energy transfer efficiency between bombarding fluorocarbon (FC) molecules and the SiO2 substrate, and discusses the limitation of securing the etch rate by high-energy FC molecules.

Negative Photo-Definable Polyimide Dry Films for Fine and High Aspect Ratio Patterning

We newly developed a negative photo-definable polyimide dry films with higher photoreactivity than conventional ones. We succeeded in fine and high aspect ratio patterning with 90 μm thickness and 8 μm width by using new polyimide dry films. When compared after curing, the tensile breaking strength and share strength of new and conventional polyimide dry films were almost the same. However, when compared after PEB and exposure, the new ones showed clearly higher properties than conventional one. Using this polyimide dry film as an inter-layer dielectrics or a permanent resist was effective in improving the wiring density of electric devices.

Sequential Infiltration Synthesis into Maltoheptaose and Poly(styrene): Implications for Sub-10 nm Pattern Transfer.

Vapor phase infiltration into a self-assembled block copolymer (BCP) to create a hybrid material in one of the constituent blocks can enhance the etch selectivity for pattern transfer. Multiple pulse infiltration into carbohydrate-based high-χ BCP has previously been shown to enable sub-10 nm feature pattern transfer. By optimizing the amount of infiltrated material, the etch selectivity should be further improved. Here, an investigation of semi-static sequential infiltration synthesis of trimethyl aluminum (TMA) and water into maltoheptaose (MH) films, and into hydroxyl-terminated poly(styrene) (PS-OH) films, was performed, by varying the process parameters temperature, precursor pulse duration, and precursor exposure length. It was found that, by decreasing the exposure time from 100 to 20 s, the volumetric percentage on included pure Al2O3 in MH could be increased from 2 to 40 vol% at the expense of a decreased infiltration depth. Furthermore, the degree of infiltration was minimally affected by temperature between 64 and 100 °C. Shorter precursor pulse durations of 10 ms TMA and 5 ms water, as well as longer precursor pulses of 75 ms TMA and 45 ms water, were both shown to promote a higher degree, 40 vol%, of infiltrated alumina in MH. As proof of concept, 12 nm pitch pattern transfer into silicon was demonstrated using the method and can be concluded to be one of few studies showing pattern transfer at such small pitch. These results are expected to be of use for further understanding of the mechanisms involved in sequential infiltration synthesis of TMA/water into MH, and for further optimization of carbohydrate-based etch masks for sub-10 nm pattern transfer. Enabling techniques for high aspect ratio pattern transfer at the single nanometer scale could be of high interest, e.g., in the high-end transistor industry.

High-integration and high-performance micro thermoelectric generator by femtosecond laser direct writing for self-powered IoT devices

Astonishing advances in IoT devices are making a revolutionary progress on smart society, but requiring for sustainable micro power sources. Micro thermoelectric generators (μTEGs) have the potential to power the IoT devices when incorporated into compact microcircuits. Nevertheless, the relatively low output of μTEGs can hardly reach the rated power and voltage for practical use at present. Herein, a femtosecond laser direct writing method is proposed for the fabrication of μTEGs with easy operation and good compatibility, and the precise adjustment of laser energy ensures a high-precision high aspect ratio pattern etch of thermoelectric films. The highly-integrated μTEG (364 pairs/cm2) meets an excellent output of 494 mV and 0.514 mW cm−2 at ΔT = 33.1 K and an efficiency factor of 0.47 μW cm−2 K−2. Eventually, it can realize an output of 3.3 V by using a power manager with the function of stabilizing and drive various electronic components, exhibiting a promising power source for self-powered IoT devices.

Anisotropic and low damage III-V/Ge heterostructure etching for multijunction solar cell fabrication with passivated sidewalls

This article presents a complete plasma etching process to etch high aspect ratio patterns on III-V/Ge solar cell heterostructure with low damage for the fabrication of multijunction solar cells with a through cell via contact architecture. A SiCl 4 /H 2 chemistry was studied with different hydrogen dilutions within the plasma (0%, up to 67%) and with different cathode temperatures (20 ∘ C, up to 200 ∘ C). This chemistry choice creates a SiCl x -based inhibiting layer on the sidewalls that promotes anisotropic etching through the epitaxial heterostructure. The study suggests that a high hydrogen flow and a low temperature reduce the chemical reactions that create sidewall erosion. A high hydrogen flow appears to provide a hydrogen passivation of the non-radiative defects on the III-V heterostructure sidewall during the etching process. III-V/Ge triple junction solar cells with standard grid line and busbar front and back contacts have been fabricated and via-holes were plasma-etched through the active layers in order to investigate the impact of hydrogen passivation on the photovoltaic performance. The results demonstrate that the hydrogen passivation enables an open-circuit voltage increase that persists even after 5 months. This plasma process can also be used for the mesa etching step on multijunction solar cells with standard contacts. Thus, it could provide an appealing pathway to increase the conversion efficiency of state-of-the-art multijunction solar cells with standard contacts. To complete the etching process, a liner is used to protect the sidewall properties and a time-multiplexed Ge etching process is proposed to finalize the patterning and even open a pathway towards III-V/Ge plasma dicing. • A complete etching process is proposed to etch deep and anisotropic vias through a III-V/Ge heterostructure. • A low temperature SiCl 4 /H 2 plasma process is well suited to etch III-V/Ge heterostructures with limited sidewall erosion. • High H 2 flow enables a defect passivation on the etched sidewalls and it persists over several months.

Structural and Mechanical Properties of Silica Mesoporous Films Synthesized Using Deep X-Rays: Implications in the Construction of Devices

In recent years, the use of X-Rays (XR) irradiation for the production of ordered mesoporous thin films has been well established. This technique allows obtaining porous materials that contain thermal sensitive moieties or nanoparticles. Additionally, in combination with lithographic masks, the generation of high aspect ratio patterns of several geometrical shapes with micrometric resolution is possible. In this work, the structural and mechanical properties of porous silica thin films obtained by sol-gel method along with the exposure to high intensity XR is presented. Two templates (CTAB and Brij 58) and several irradiation doses and post-synthesis treatments were evaluated by a combination of characterization techniques, including grazing incidence small-angle XR scattering, electronic microscopies, XR reflectometry and nanoindentation. The results demonstrate that all the irradiated oxides presented a highly ordered mesoporous structure, independently of the XR dose and post thermal treatment. Their mechanical properties, on the other hand, clearly depend on the irradiation dose; high hardness values were measured on samples irradiated at low doses but higher doses are necessary to obtain films with indentation modulus values similar to the obtained for thermally treated coatings. The accessible porosity, essential for the application of these films in devices for micro- and nanofluidics, is also dependent on the dose and the thermal treatment performed afterward. The same tendency is observed for the films contraction and rigidity. After this characterization, it was concluded that thermal treatments are needed after the consolidation with XR to increase the accessibility and structural integrity of these porous oxides. Finally, the production of composites with metallic (Au and Ag) nanoparticles was tested which envisioned their applications in sensing and catalysis. Moreover, diverse geometrical patterns of both pure and Ag nanoparticles doped silica mesostructured films were obtained, demonstrating the feasibility of the proposed approach. The results presented in this work are of great importance to understand the transport mechanisms that operate in these silica porous films, in order to integrate them in different devices for lab-on-a-chip applications.

Tribological response of laser-textured steel pins with low-dimensional micrometric patterns

Our purpose was to study the tribological effects of surface texturing at the mesoscale, generally disregarded. We realized hemispherical dimples on 100Cr6 steel pins using a ns-pulsed Nd:YAG laser. Both radius and depth of the patterns fall in the very-low part of the micrometric scale, ranging respectively from 10 to 13 μm and from 4 to 6.5 μm. To map Stribeck curves, we used a pin-on-disk apparatus and a commercial motor oil as lubricant. The results confirm that the post-texturing lapping process is crucial to achieve a reduction in the coefficient of friction. These patterns show a tribological effect mainly in mixed lubrication regime, and partially in hydrodynamic regime. Even very small differences in radius and depth may induce very different response, evidencing the need of very fine tuning of the geometrical characteristics of the patterns. The lower friction was recorded for larger and deeper dimples. Friction reduction for increasing dimples density has been found as well. Endurance tests in boundary lubrication regime show a more stable coefficient of friction and a larger mean lifetime of patterned surfaces with respect to polished one. Furthermore, water-contact-angle tests show a weak hydrophobic effect for high aspect ratio patterns. However, no correlation was observed between wettability and tribological response.

UV Projection Scanner Performance in Thick Resists for High Aspect Ratio Cu Pillars

Integration in the third dimension is becoming increasingly more common in advanced packaging to overcome limitations in Moore's Law. One popular example for 3D Integration is Package-on-Package (PoP), where memory stacks are mounted above the processor. This approach requires tall, high density Cu pillars for interconnection around the processor. Ever increasing I/O requirements creates a need for Cu pillars with smaller critical dimension (CD) in thick resist. This creates high aspect ratio challenges for materials and equipment. For lithography tools, low NA projection systems are fundamentally well-suited to achieve high aspect ratio patterns, due to the inverse relationship between depth-of-focus (DOF) and Numerical Aperture (NA). However, the NA of low NA steppers is not low enough for thick resists. The full-field projection scanner with lower NA provides superior performance than the stepper counterpart at higher throughput and lower cost. This paper presents the high aspect ratio performance of the full-field UV projection scanner tool in various thick resists ranging from 50um to 300um film thickness. Aspect ratios as high as 20:1 are demonstrated for square vias with 1:1 pitch. Further, as feature resolution is only practical with alignment, the alignment of thick resists is also included.

Molecular Glass Photoresists with High Resolution, Low LER, and High Sensitivity for EUV Lithography

AbstractNovel molecular glasses (MGs) containing bisphenol A backbone (BPA‐6 and BPA‐10) are synthesized and characterized. BPA‐6 and BAP‐10 are excellent amorphous materials for extreme ultraviolet (EUV) patterning applications with good thermal stability (Td more than 160 °C). The MGs can be used as positive‐tone photoresists combined with triphenylsulfonium perfluoro‐1‐butanesulfonate and trioctylamine dissolved in propylene glycol monomethyl ether acetate. High‐resolution feature sizes as small as 23.1 nm with extremely low line edge roughness (less than 2 nm), high sensitivity (less than 20 mJ cm−2), and good high aspect ratio patterns are obtained by using EUV lithography.

Nano-Structures Stiction Suppression by Molecular Structure Optimized Surface Energy Reduction Agent

Scaling of semiconductor devices has caused nano-structure stiction issues during the drying step of wafer cleaning. We have already proposed a surface modification process to reduce the surface energy, and we have demonstrated this process is more effective for preventing nano-structure stiction than conventional IPA (isopropyl alcohol) drying. In this paper, the proper molecular structure is investigated for surface modification agents. It is important for the suppression of stiction to reduce a surface free energy rather than to increase a water contact angle. We have attained stiction free drying of a high aspect ratio pattern with 15 nm half pitch line and space using agents with shorter alkyl groups.

Numerical study on the shrinkage behavior of SU-8 patterns

SU-8 is becoming increasingly important for fabrication of mechanical, biological and chemical mini-devices. However, SU-8 suffers from high shrinkage during curing and postbake process. It is crucial to analyze the shrinkage behavior of the SU-8. In this article, the shrinkage behavior of different SU-8 patterns was studied by a developed finite element method. A variety of concave and convex patterns (grooves, lines, pillars and holes) is simulated for 1/8 and 8 aspect ratios. The shrinkage of the patterns with different shapes and the shrinkage of the patterns with different aspect ratio were compared. The numerical simulation results show that to fabricate SU-8 structures with low shrinkage, the following patterns should be firstly considered. (1) Convex pattern, (2) high aspect ratio pattern (aspect ratio of larger than 2), and (3) circular pattern. It is expected that the proposed simulation method has a high potential for the analysis of the shrinkage process for SU-8 patterns.

Fabrication of high aspect ratio nanoscale periodic structures by the soft X-ray interference lithography

Nanoscale periodic structures have been utilized in the scintillator field to obtain enhanced light extraction efficiency. Sufficient structure depth is necessary to achieve better extraction efficiency. Recently, a soft X-ray interference lithography (SXIL) has been developed in the Shanghai Synchrotron Radiation Facility (SSRF). SXIL can be used to fabricate a high aspect ratio pattern due to the uniform distribution of the beam dose at the photoresist depth. A grating mask with a new photon stop layer was attempted, mainly consisting of Perm alloy, and it was optimized for the SXIL to increase the entire service life. Preliminary results suggest that PMMA structure with an aspect ratio of up to 3 has been successfully manufactured using SXIL techniques. Therefore, this technique has been studied to fabricate the artificial nanostructure on the scintillator in the high efficiency radiation detector area.

Nanoscale tomographic reconstruction of the subsurface mechanical properties of low-k high-aspect ratio patterns

In this work, intermittent contact resonance atomic force microscopy (ICR-AFM) was performed on high-aspect ratio a-SiOC:H patterned fins (100 nm in height and width from 20 to 90 nm) to map the depth and width dependencies of the material stiffness. The spatial resolution and depth sensitivity of the measurements were assessed from tomographic cross-sections over various regions of interest within the 3D space of the measurements. Furthermore, the depth-dependence of the measured contact stiffness over the scanned area was used to determine the sub-surface variation of the elastic modulus at each point in the scan. This was achieved by iteratively adjusting the local elastic profile until the depth dependence of the resulted contact stiffness matched the depth dependence of the contact stiffness measured by ICR-AFM at that location. The results of this analysis were assembled into nanoscale sub-surface tomographic images of the elastic modulus of the investigated SiOC:H patterns. A new 3D structure-property representation emerged from these tomographic images with direct evidence for the alterations sustained by the structures during processing.

Study on the impact of silicon doping level on the trench profile using metal-assisted chemical etching

Metal-assisted chemical etching (MACE) has been used as a promising alternative method to fabricate micro/nano-structures on silicon substrates inexpensively. In this paper, profiles of deep trenches on silicon substrates, with different doping levels, fabricated by MACE were studied. A layer of interconnected gold islands was first deposited onto the silicon substrate as catalyst. Electrochemical etching was then performed in a hydrofluoric acid (HF) and hydrogen peroxide (H2O2) mixture solution with different HF-to-H2O2 ratio ρ (ρ = [HF]/([HF] + [H2O2])). Vertical deep trenches were fabricated successfully by using this method. It was observed that even under identical experimental condition, sidewalls with various tilting angles and different morphology could still form on silicon substrates with different resistivity. This possibly because with different resistivity silicon substrate, the gradient of holes in it greatly changed, and so did the final morphology. As a result, the tilting angle of etched trench sidewall can be tuned from 6° to 96° using silicon substrates with different resistivity and etchants with different ρ. By applying the angle-tuning technique revealed in this study, high aspect ratio patterns with vertical sidewalls could be fabricated and three-dimensional complex structures could be designed and realized in the future.

High aspect ratio patterning of photosensitive polyimide with low thermal expansion coefficient and low dielectric constant

A photosensitive polyimide system based on amine catalyzed imidization of a precursor poly(amic ester) is described. The material is based on the meta ethyl ester of pyromellitic dianhydride and 2,2’ bis(trifluoromethyl)benzidine. It acts as a negative tone resist when formulated with a photobase generator. The material exhibits a dielectric constant of 3.0 in the gigahertz range, a coefficient of thermal expansion of 6±2 ppm/K, and can be patterned to aspect ratios of >2 when formulated with a highly quantum efficient cinnamide type photobase generator.

Advanced Plating Photoresist Development for Semiconductor Packages

In recent years, novel electronic products like mobile phones, tablets, and personal computer have shrunk dramatically and become highly functionalized. To satisfy these market trends of smaller thinner devices, packaging technologies such as 3D-TSV, 2.5D, PoP and Flip-chip wafer bumping are being used. We have developed negative tone resists for re-distribution layer, C4 and micro bumps. Our resist is negative tone resist which incorporates an acrylate cross-linker system with photo radical initiator. This formulation shows excellent chemical resistance to various plating solutions such as Cu, Ni, Sn/Ag and Au, with good stripability. The key technology of plating resists for advanced packages is high resolution, allowing for high aspect ratio patterning capability that covers a wide range of film thicknesses. An example of such applications is in advanced PoP package design which require a thick film material that has high resolution capability, along with high aspect ratio performance. Additionally, high resolution re-distribution layer resists can be used to create fine pitch conditions which are necessary for package downsizing. Our resist shows good patterning performance from below 10 μm to above 100 μm film thickness conditions. In this paper, material design and key properties of novel plating resist with high resolution and high aspect ratio performance with a wide range film thickness ranges are discussed.

A Fundamental Study of the Electron Beam Lithography beyond Sub 100nm Process and its Application

It is well known that electron beam lithography is one of the potential candidates to fulfill of the demand of the miniaturization of the design rule of semiconductor integrated circuits beyond sub 100nm size with high reproducibility. It is also a fact that the resolution is recognized to depend on the various factors which are oriented to the machine and process conditions, for example, electron beam diameter, the intensity distribution of the beam itself, the resistance properties polymers, the development conditions, etc. Therefore, it is thought that it is impossible to be derivable directly and unambiguously from the resist material itself. In this study, the intrinsic resolution of the resist polymer was discussed based on the hypothesis that the resolution itself may be able to improve to the same size as the size of an electron beam profile, or less. The bi-layer structure ZEP520A/poly methyl glutar imide (PMGI) was proposed and tested. As for the results achieved, the contrast γ was improved constantly with a reduction in the development time and a decrease in the development temperature. The highest γ value, approximately 18, was obtained during development at the-20°C condition. An approximately 70nm with high aspect ratio pattern which is almost the same size of the beam pattern was obtained. This result provides an understanding how the intrinsic resolution of the resist material should be, and can be applied to other lithography methods. This process was applied to the actual electrode pattern making process. An approximately 100nm width of Copper nanowire as the gate electrode for the AlGaN/GaN HFET was successfully demonstrated. In addition, AlGaN/GaN HFET operated at about 73.5GHz, successfully.

Origin of high propagation loss in electrospun polymer nanofibers

We evaluate optical propagation loss (α) in electrospun poly(methyl methacrylate) (PMMA) nanofibers with different wavelength (λ) and determine the origin of the loss. Aligned single electrospun nanofibers composed of PMMA and a small amount of an organic dye are fabricated with an average diameter of approximately 640 nm. After cladding seven fiber samples, α is evaluated to be 26–62 dB cm−1 at wavelengths 590−680 nm. Moreover, α depended linearly on λ−4, and from the fitting functions we determined the ratio of the following two possible losses for α: loss at the interface between the fiber-core and cladding because of non-uniformity within the fibers (αun), and loss because of excess light scattering in the fibers resulting from density inhomogeneity of PMMA (αsc). For the fibers, αun is evaluated to be 6.9–22 dB cm−1, which represents 19%–50% of α at λ of 650 nm with α ∼ αun + αsc. Thus, we conclude that the high α in these fibers originates from both their poor uniformity and density inhomogeneity. Furthermore, a quantitative investigation of uniformity in the individual fibers revealed that the root mean square roughness ranges from 5.5 nm to 9.0 nm and the theoretical value of αun was ∼1 dB cm−1 showing reasonable agreement with experimental data. These findings hold for low-loss polymer nanofiber waveguides, which have high aspect ratio and fine patterning even in three dimensions.

A degradable polycyclic cross-linker for UV-curing nanoimprint lithography

In this paper, we design and synthesize a degradable polycyclic diacrylate cross-linker, 2,10-diacryloyloxymethyl-1,4,9,12-tetraoxaspiro[4.2.4.2] tetradecane (DAMTT), from easily available starting materials by bis-ketalization of 1,4-cyclohexanedione with glycerol, followed by esterification with acryloyl choride. The chemical structure of the degradable cross-linker is characterized by FTIR, 1H NMR and GC-MS. A UV-NIL resist based on DAMTT has a very low shrinkage (about 2.5%) and a high Young's modulus of 1.89 GPa after UV-curing, and is soluble in acidic media. Patterns with sub-10 nm resolution are faithfully imprinted into the DAMTT film. The degradable cross-linker is incorporated with a multifunctional acrylated siloxane to increase O2 RIE resistance as an etch barrier for high aspect ratio pattern transfer. The cross-linked film of the UV-curable resist remains soluble in acidic media even though its formulation contains acrylated siloxane up to 50% (w/w). Moreover, in contrast to most UV-NIL resists which are insoluble in solvents after curing, the DAMTT resist can independently achieve a lift-off process without the assistance of a thermoplastic polymer layer. That makes it possible to fabricate metal nanostructures on highly curved surfaces via a hybrid UV-curing nanoimprint technique. For example, metal gratings are successfully fabricated on the cylindrical surface of an optical fiber via a lift-off process.