Dry Etch Rates Research Articles

Understanding Growth Mechanism of Atomic Layer Deposition of Tisiox for Spacer in Double Patterning Process

The aggressive scaling down of patterning technology in semiconductor industry is challenging owing to the limitation of current extreme ultraviolet EUV lithography technique, thus applying self-aligned double patterning (SADP) is essential. In this regard, TiSiOx may be a promising spacer material for SADP, which is beneficial to tolerate high aspect ratio structure triggered by shrinkage in patterning size. However, atomic layer deposition (ALD) of quaternary materials is usually faced to unexpected growth characteristics leading to undesired film qualities, while precise control of thickness and film properties is vital to achieve SADP. This work provide understanding of how growth characteristics of ALD TiSiOx are deviated according to process temperature. At 100 °C, hygroscopic TiSiOx surface which is originated by the presence of Ti-O-Si bond is exposed to H2O by-product leading to enhanced growth rate of TiSiOx compared to ideal case. If the process temperature is increased to 200 °C, opposite behavior is observed since hygroscopic TiSiOx surface characteristic is no more dominant to growth rate of ALD TiSiOx due to dehydroxylation. Theses nonconventional growth characteristics dramatically influence on hydroxyl concentration in TiSiOx films resulting in different spacer qualities such as dry etch rate and elastic modulus. These correlative results suggest that the process conditions should be modulated to suppress hydroxyls incorporation into growing TiSiOx surface during ALD to obtain a high-quality TiSiOx thin films for SADP.

Role of a surface hydroxyl group depending on growth temperature in atomic layer deposition of ternary oxides

Atomic layer deposition (ALD) of multicomponent materials is challenging because the growth characteristics often deviate from what is expected due to the difference in surface characteristics of heterogeneous and single materials, resulting in undesired thickness or properties. For metal oxides, the growth characteristics highly rely on the surface hydroxyl groups, which play a role as the reactive site. Thus, studying the reaction mechanism of a precursor on hydroxyl-terminated heterogeneous surfaces is important for understanding the nonideal growth of ternary oxide. Here, we investigated the correlation between hydroxyl and the growth of ALD TiSiOx depending on temperature, analyzing infrared spectra, and chemical compositions. The results show that large amounts of hydroxyl are detected in TiSiOx deposited at 100 °C, where the adsorption of H2O on Ti–O–Si bonds is favorable. It leads to higher growth per cycle (GPC) than the estimated value. In contrast, the hydroxyl disappears at 200 °C due to dehydroxylation, resulting in lower GPC. Differences in hydroxyl also influence the film density as revealed in x-ray reflection spectra, which is related to the film qualities (e.g., elastic modulus and dry etch rates). This work provides insight into how to control hydroxyl in the ALD of ternary oxides, which is susceptible to hydroxyl incorporation, leading to undesired growth characteristics.

Synthesis and characteristics of Sn-doped SiO2 via plasma-enhanced atomic layer deposition for self-aligned patterning

Sn-doped SiO2 thin films as a spacer for self-aligned patterning were deposited by plasma-enhanced atomic layer deposition and their characteristics were evaluated. This doping research was conducted to improve the mechanical properties of SiO2 films, which have been conventionally used as a spacer material. Because pure SiO2 films have a low Young's modulus, the pattern is stretchable and may collapse as the patterning size decreases. The ratio of the SnO2 and SiO2 deposition cycle was varied from 15(SiO2):1(SnO2) to 3(SiO2):1(SnO2) to modify the film characteristics. X-ray reflectivity (XRR) and time-of-flight secondary ion mass spectrometer analyses revealed whether Sn was doped in SiO2 or became a nanolaminate. The x-ray photoelectron spectroscopy analysis showed that a greater amount of Sn in the SiO2 thin film resulted in a binding energy shift toward the lower binding energy Si2p and Sn3d peaks, and more Si–O–Sn chemical bonding, which increased the number of stiffer ionic bonds as the SnO2 cycle ratio was increased. Therefore, Young's modulus measured by using a nanoindenter increased from 39.9 GPa for SiO2 films to 90.9 GPa for 3(SiO2):1(SnO2) films. However, the hardness results showed a different tendency due to the not well-distributed nanolaminate film structure showing a tendency to decrease and then increase as doping increases. Moreover, the growth rate and film density were evaluated by XRR. The growth per cycle (GPC) of SiO2 was 1.45 Å/cycle and the GPC of SnO2 was 1.0 Å/cycle. The film density of SiO2 was 2.4 g/cm3 and the film density of SnO2 was 4.9 g/cm3. Also, the GPC and film density values of the Sn-doped SiO2 films were in between the values of pure SiO2 and SnO2. The dry etch rate was also measured by reactive ion etching using CF4 plasma with 150 W for 1 min.

Cascaded Ni hard mask to create chlorine-based ICP dry etched deep mesas for high-power devices

A highly selective cascaded Ni hard mask without stress and film damage issues suitable for the formation of deep vertical mesas for high-power devices is presented. A Cl2/BCl3/Ar inductively coupled plasma dry etch was used to investigate the effect of photoresist, and patterned Ni hard masks applied via four different methods on the etch rate of GaN, and mask selectivity. Strain in the e-beam only deposited Ni films produced low yield due to poor adhesion. Electroplated Ni showed rough mask morphology. Sputtered Ni left damage/chemically reacted layers on the GaN under the mask. A cascaded 50 nm e-beam evaporated Ni followed by 2 µm of sputtered Ni mask method improved the yield to 100%, achieved high selectivity and retained an undamaged GaN surface morphology. The cascaded Ni hard mask successfully achieved GaN mesas up to 13 µm. The dry etching rates of the photoresist, GaN and Ni masks were 250, 275 and 13 nm min−1, respectively giving an etch selectivity of the GaN/Ni hard mask of ∼20, much higher than the etch selectivity of 1.1 for the photoresist. Furthermore, yield of the cascaded Ni hard mask was 100% making it suitable for commercial high-power electronics.

Step Coverage and Dry Etching Process Improvement of Amorphous Carbon Hard Mask

Amorphous carbon hard mask (ACHM) films have been widely applied as protective components and hard etching masks in lithography and dry etching processes. The capability of lithography is directly dependent on the step coverage (SC) of the ACHM. Poor SC may impact the protection of device patterns during the etching process and lead to overlay marks occurring in lithography. In this work, the ACHM film processing process is engineered and optimized towards better SC through the comparative study of the C2H2 and C3H6 precursors at different temperatures. Furthermore, a process parameter design of experiment (DOE), with C2H2 as a precursor to optimize the dry etching rate, is proposed. The results of the experiment show that the dry etching performance is enhanced by higher power, temperature and C2H2 flow, and a smaller gap, lower pressure and lower carrier gas flow. A selective etching ratio of SiO2 and SiN, with an improved process window, is obtained. ACHM film elimination process is also validated by characterizing the surface roughness. The demonstrated results can be instructive in terms of the optimization of etching process in future semiconductor manufacturing.

Using block-copolymer nanolithography as a tool to sensitively evaluate variation in chemical dry etching rates of semiconductor materials with sub-5 nm resolution

Ion implantation is a robust and established method to customize the electronic properties of Si. However, fabricating doped, ultrafine semiconductor nanostructures can be challenging. Ion implantation has well-established effects on the dry etch rates of Si, which becomes increasingly consequential as the target dimension shrinks below a few tens of nanometers. While dry etching arrays of block copolymer-templated nanoscale holes (pitch = 37.5 nm, diameter ∼25 nm) into p-type, n-type, and undoped Si, we observed that the lateral etch rate was notably larger for the n-type regions than p-type or undoped regions. By doing image analyses on high resolution electron micrographs of the nanostructured hole arrays, we were able to extract the porosity and average radii of the holes with subnanometer sensitivity and compare the relative etch rates between different doping conditions. We found that degenerately doped n-type silicon consistently etches between approximately 17% and 27% faster in the lateral direction than p-type Si, resulting in significantly larger porosity and, consequently, less mechanical stability. Here, we demonstrate that top-down dimensional analysis of a densely packed porous nanostructure is a robust method for assessing extremely small differences in the lateral, chemical etch rate of doped Si to a degree of sensitivity that was previously unachievable. The minute, dense-packed nature of block copolymer self-assembled nanostructures is shown to be ideal for this application. This proposed method could be useful for designing fabrication processes for heterogeneous nanostructures, as slight dry etch rate variations that may be within process tolerance at the micrometer-scale appear to have nontrivial consequences at the nanometer scale.

Process Optimization of Amorphous Carbon Hard Mask in Advanced 3D-NAND Flash Memory Applications

Amorphous carbon hard mask (ACHM) films are widely used as etching hard masks in 3D-NAND flash memory, which has put forward higher requirements in the film deposition rate, film transparency, uniformity, and selective etching. In this work, the ACHM film processing is engineered and optimized by comparatively studying acetylene (C2H2) and propylene (C3H6) as carbon sources at the different temperatures of 300 °C, 350 °C and 400 °C. By increasing the deposition temperature, the deposition rate, non-uniformity, and dry etch rate of ACHM are improved at the penalty of a slightly increased extinction coefficient of the film, due to lower incorporation of hydrocarbon reactants absorbed into film at higher temperatures. However, the Fourier transformation infrared (FTIR) spectrum intensity is decreased with the increase of the deposition temperature. The lower dry etch rate of ACHM is achieved by using C3H6 as a carbon source deposited at 400 °C. The best dry etch selective ratio values are also achieved with 10.9 and 9.5 for SiO2 and SiN, respectively. These experimental results can be very promising in the advancement of etching process in 3D-NAND applications.

The relationship between the Young's modulus and dry etching rate of polydimethylsiloxane (PDMS).

Polydimethylsiloxane (PDMS) has been the pivotal materials for microfluidic technologies with tremendous amount of lab-on-a-chip devices made of PDMS microchannels. While molding-based soft-lithography approach has been extremely successful in preparing various PDMS constructs, some complex features have to been achieved through more complicated microfabrication techniques that involve dry etching of PDMS. Several recipes have been reported for reactive ion etching (RIE) of PDMS; however, the etch rates present large variations, even for the same etching recipe, which poses challenges in adopting this process for device fabrication. Through systematic characterization of the Young's modulus of PDMS films and RIE etch rate, we show that the etch rate is closely related to the polymer cross-link density in the PDMS with a higher etch rate for a lower PDMS Young's modulus. Our results could provide guidance to the fabrication of microfluidic devices involving dry etching of PDMS.

Oxide Removal from the InSb Plate Surface to Produce Lateral Spin Valves

The formation conditions of a smooth and oxide-free surface of InSb semiconductor with the purpose of fabricating lateral spin devices based on it are investigated. The dry etching rate by Ar ions of the surface of the crystalline faces (100) of InSb plates as well as a variation in their roughness depending on the power supplied to ion etching devices are investigated. The degree of oxidation of the semiconductor surface exposed to air after ion cleaning and annealing in molecular hydrogen are evaluated. Based on comparison of the efficiency of spin injection in devices formed with semiconductors subjected to various types of treatment, a conclusion is made about the parameters of optimal preparation of the surface of the InSb wafers for the fabrication of lateral spin devices.

Очистка от оксидов поверхности пластин полупроводника InSb для создания латеральных спиновых клапанов

AbstractsThe formation conditions of a smooth and oxide-free surface of InSb semiconductor with the purpose of fabricating lateral spin devices based on it are investigated. The dry etching rate by Ar ions of the surface of the crystalline faces (100) of InSb plates as well as a variation in their roughness depending on the power supplied to ion etching devices are investigated. The degree of oxidation of the semiconductor surface exposed to air after ion cleaning and annealing in molecular hydrogen are evaluated. Based on comparison of the efficiency of spin injection in devices formed with semiconductors subjected to various types of treatment, a conclusion is made about the parameters of optimal preparation of the surface of the InSb wafers for the fabrication of lateral spin devices.

Electrical contact uniformity and surface oxidation of ternary chalcogenide alloys

Uniform metal contacts are critical for advanced thermoelectric devices. The uniformity of the contact resistance for gold, tungsten, and SrRuO3 electrodes on polycrystalline ternary Bi2Te3-based alloys for different types of surface cleaning procedures was characterized. The presence of a nanometer-thick native oxide layer on the Bi2Te3 surface leads to large and non-uniform contact resistance. Surface treatments included solvent cleans and chemical and dry etching prior to metallization of the Bi2Te3. Only etching the surface led to a significant improvement in contact resistance uniformity. None of the tested contacts reacted with the underlying Bi2Te3 substrate. Etching resulted in the removal of the native oxide on the Bi2Te3 surface, which was characterized using X-ray photoelectron spectroscopy (XPS). The average thickness, chemistry, and dry etch rate of the native oxide was further characterized using XPS. The non-uniformity in contact resistance suggests that the native oxide grows non-uniformly on polycrystalline bismuth telluride surfaces.

(Invited) ScAlN: A Novel Barrier Material for High Power GaN-Based RF Transistors

ScAlN is a novel group IIIA/IIIB-N alloy gaining interest for acoustoelectric applications. The high piezoelectric coefficients that make ScAlN appealing for RF filters combined with high spontaneous polarization have the potential to open up a new class of microwave and millimeter-wave high-electron-mobility transistors (HEMTs) with high channel sheet charge density when ScAlN is used as the barrier layer. We present growth of ScAlN using molecular beam epitaxy (MBE) with an electron beam Sc source and show initial channel transport measurements. These initial demonstrations suggest MBE can be employed to grow ScAlN with sufficient crystal quality and chemical purity for use in electronic devices. ScAlN dry etch rates using standard Cl2-based reactive ion etching are much slower than AlN and GaN, enabling the use of ScAlN as a fluorine-free etch-stop layer. A simplified etch-stop process will enable passivation and gate recess processes to improve breakdown and reduce dispersion in RF HEMTs.

Surface heterogeneity in KTaO3 (001)

Surface heterogeneity in Ar+ ion bombarded samples of (001) oriented KTaO3 was studied using (in-situ) electron microscopy and atomic force microscopy. Ion bombardment results in surface damage as well as in off-stoichiometry of K and Ta due to the large differences in atomic radii of the two constituent elements and hence different dry etching rates. Subsequent annealing of such samples reduces the potassium content via vaporization and results in the formation of tantalum-rich secondary phases on the surface. The phase that segregates on the surface is dependent on the oxygen partial pressure, annealing temperature as well as K:Ta stoichiometry. However, samples etched with chemical means to remove lattice damage and surface disorder prior to annealing exhibit little to no surface heterogeneity.

Ultraviolet-Assisted Release of Microelectromechanical Systems From Polyimide Sacrificial Layer

Process heating of microelectromechanical systems (MEMSs) devices hardens polyimide sacrificial layers, complicating the final release and lowering yield for delicate structures. This paper reports ultraviolet (UV)-assisted release, which is demonstrated on an MEMS cantilever fabricated by an eight-mask photolithographic process. A commercial co-developable polyimide ProLift 100 (Brewer Science) sacrificial layer was used. The process subjects the device to multiple heat treatment steps. Both wet chemical etching and dry reactive ion etching were explored. During the former, large sheets of hardened polyimide floated free of the substrate to damage delicate MEMS structures. The latter is typically slow, so that grass appears during long exposures to plasma ions. The solution reported here is UV exposure prior to release. Optical constants of the sacrificial layer material, which were baked to simulate thermal histories during various fabrication steps, were measured to understand the effectiveness of UV exposure. Wet and dry etch rates were measured as a function of UV dose. Finally, the advantages of UV pretreatment were demonstrated during the release of actual MEMS cantilevers. [2015-0193]

Nanowire polarizers by guided self-assembly of block copolymers

Wire-grid polarizers (WGPs) are currently limited by their wafer-scale manufacturing methods to sizes of approximately 12 to 18 in. For large-size displays, a new method for the production of large-area WGPs is required. Large-area WGPs were simulated using the finite-difference-time-domain method, and a scaleable method for their production based on a block copolymer (BCP)-nanostructured template was implemented. The nanostructured template is globally aligned through the use of a cylinder-forming liquid crystal (LC) diblock copolymer, which is first aligned on a rubbed polyimide substrate. A surface-relief template is produced using the differential dry etch rates of the cylinder-forming component and LC polymer matrix component of the BCP. The template is metalized to produce a WGP. Polarizers of arbitrary size with polarization efficiency up to 0.6 have been made in close agreement with calculated values for idealized structures. The choice of the cylinder-forming polymer is critical to the degree of alignment of the template, and the thermal stability of the LC polymer matrix is critical to the stability of the template during etching.

Micropatterning PEDOT:PSS layers

PEDOT:PSS is a conductive polymer that is used as electrodes in organic electronic devices, but also in neuronal probes and implantable devices. This material can also be used for building deformable electrodes in soft substrates for several sensing applications. However, this material being sensitive to several chemicals and moisture it is difficult to pattern microstructures using standard lithography techniques. This paper will review and show some techniques developed for patterning PEDOT:PSS thin films using both soft lithography, such as microcontact printing and shadow masking, and conventional lithography techniques. In addition of this review we present a new lithography technique using silicon nitride protection layer and an analysis and comparison of ICP RIE dry plasma etch rates of PEDOT:PSS with different gases.

Effect of deposition temperature and thermal annealing on the dry etch rate of a-C: H films for the dry etch hard process of semiconductor devices

The effect of deposition and thermal annealing temperatures on the dry etch rate of a-C:H films was investigated to increase our fundamental understanding of the relationship between thermal annealing and dry etch rate and to obtain a low dry etch rate hard mask. The hydrocarbon contents and hydrogen concentration were decreased with increasing deposition and annealing temperatures. The I(D)/I(G) intensity ratio and extinction coefficient of the a-C:H films were increased with increasing deposition and annealing temperatures because of the increase of sp2 bonds in the a-C:H films. There was no relationship between the density of the unpaired electrons and the deposition temperature, or between the density of the unpaired electrons and the annealing temperature. However, the thermally annealed a-C:H films had fewer unpaired electrons compared with the as-deposited ones. Transmission electron microscopy analysis showed the absence of any crystallographic change after thermal annealing. The density of the as-deposited films was increased with increasing deposition temperature. The density of the 600°C annealed a-C:H films deposited under 450°C was decreased but at 550°C was increased, and the density of all 800°C annealed films was increased. The dry etch rate of the as-deposited a-C:H films was negatively correlated with the deposition temperature. The dry etch rate of the 600°C annealed a-C:H films deposited at 350°C and 450°C was faster than that of the as-deposited film and that of the 800°C annealed a-C:H films deposited at 350°C and 450°C was 17% faster than that of the as-deposited film. However, the dry etch rate of the 550°C deposited a-C:H film was decreased after annealing at 600°C and 800°C. The dry etch rate of the as-deposited films was decreased with increasing density but that of the annealed a-C:H films was not. These results indicated that the dry etch rate of a-C:H films for dry etch hard masks can be further decreased by thermal annealing of the high density, as-deposited a-C:H films. Furthermore, not only the density itself but also the variation of density with thermal annealing need to be elucidated in order to understand the dry etch properties of annealed a-C:H films.

Microlens array production in a microtechnological dry etch and reflow process for display applications

The fabrication of arrays consisting of densely ordered circular convex microlenses with diameters of 126 µm made of quartz glass in a photoresist reflow and dry etch structure transition process is demonstrated. The rectangular lens arrays with dimensions of 6 mm × 9 mm were designed for focussing collimated light on the pixel center regions of a translucent interference display, which also was produced in microtechnological process steps. The lenses focus light on pixel centers and thus serve for increasing display brightness and contrast since incoming collimated light is partially blocked by opaque metallic ring contacts at the display pixel edges. The focal lengths of the lenses lie between 0.46 mm and 2.53 mm and were adjusted by varying the ratio of the selective dry etch rate of photoresist and quartz glass. Due to volume shrinking and edge line pinning of the photoresist structures the lenses curvatures emerge hyperbolic, leading to improved focussing performance.

Comparative study on the properties of amorphous carbon layers deposited from 1-hexene and propylene for dry etch hard mask application in semiconductor device manufacturing

Amorphous carbon layers (ACLs) were prepared by plasma enhanced chemical vapor deposition (PECVD) from 1-hexene (C 6H 12) and propylene (C 3H 6) as a carbon source at different temperatures for dry etch hard mask of semiconductor devices manufacturing process. The deposition rate of ACL deposited at 550 °C from C 6H 12 and C 3H 6 was 5050 Å/min and 6360 Å/min. Although the deposition rate of ACL deposited from C 6H 6 was lower than that from C 3H 6, normalized deposition rate of ACL deposited from C 6H 12 was 1.64 times higher than that from C 3H 6. The relative amount of hydrocarbon contents measured by FTIR (Fourier transformation infrared) and TDS (thermal desorption spectroscopy) was decreased with the increase of deposition temperature. Raman results showed that the numbers and size of graphite cluster of ACLs deposited from each source were increased with the increase of deposition temperature. The extinction coefficient of ACL deposited at 550 °C from C 6H 12 was 0.51 and that from C 3H 6 was 0.48. The density of ACL deposited at 550 °C from C 6H 12 was 1.48 g/cm 3 and that from C 3H 6 was 1.45 g/cm 3. The dry etching rate of ACL deposited at 550 °C from C 6H 12 was 1770 Å/min and that from C 3H 6 was 1840 Å/min. The deposition rate, dry etch rate and the amount of hydrocarbon contents of ACLs deposited from each carbon source were decreased with the increase of deposition temperature but extinction coefficient and density were increased with the increase of deposition temperature. We concluded that the variation behavior of the deposition characteristics and film properties of ACLs from C 6H 12 with the increase of deposition temperature was the same as those of ACLs from C 3H 6. The high density and low dry etch rate of ACL from C 6H 12 can be explained by less hydrocarbon incorporation during deposition and these properties are more favorable for the dry etch hard mask application in semiconductor device fabrication.

Highly Controlled Wet and Dry Etching of Gallium Doped (Mg, Zn) O Epilayers Grown Using Metalorganic Vapor Phase Epitaxy

The wet and dry etch rates of Ga-doped ZnO and MgxZn1-xO deposited on r-plane sapphire by metalorganic vapor phase epitaxy (MOVPE) were studied for magnesium content 0 ≤ x ≤ 0.3 using dilute phosphoric acid and halogen–based inductively coupled plasma reactive ion etching (ICP-RIE) respectively. A decrease in the dry etch rates with increasing magnesium content was observed along with relatively low thermal activation energies of 21, 25, and 55 meV corresponding to n-ZnO, n-Mg0.1Zn0.9O, and n-Mg0.3Zn0.7O films respectively. Conversely, wet etch rates increased with increasing magnesium content with corresponding thermal activation energies of 8.4, 5.5, and 4.3 kCal/mol for n-ZnO, n-Mg0.05Zn0.95O, and n-Mg0.1Zn0.9O epilayers respectively. The dominant rate-limiting step was determined to be ion-assisted desorption of the etch products including (Mg, Zn) Cl2 during ICP-RIE etching and the wet etch process transitioned from reaction rate-limited to diffusion rate-limited etching with increasing magnesium content.