Silicon Nitride Etching Research Articles

Nitride etching with hydrofluorocarbons. I. Selective etching of nitride over silicon and oxide materials by gas discharge optimization and selective deposition of fluorocarbon polymer

Selective etching of silicon nitride over silicon and silicon oxide is one of the most critical processes in the fabrication of complementary metal–oxide–semiconductor devices. In a typical spacer process, the gate is electrically isolated from the source and drain region by the deposition of thin nitride. A plasma etch is employed to remove the nitride from the source/drain regions without or with minimal damage to the exposed surfaces. The authors show that the typical plasma process that enables this process is based on the oxidation rate of silicon and has many limitations when applying this process to devices of 30 nm critical dimension (CD) or lower. The authors show novel gas discharges with which nitride can be etched differently, in particular, because the etch rates are controlled by selective polymer deposition. The novel etch mechanism is explained in detail and advantages and challenges are discussed, in particular. Selected studies of the feedgas chemistry lead to optimized dissociation as evidenced by the respective etch selectivities. The authors demonstrate that the novel etch mechanism is able to reduce nitride thinning and substrate damage significantly, enabling further pitch and CD scaling of spacer etch when employing this novel chemistry C4H9F. The authors also show that because of these advantages, the novel chemistry is a very promising candidate to enlarge the process window for spacer processes of nonplanar devices.

Quasiatomic layer etching of silicon nitride with independent control of directionality and selectivity

Atomic layer etching has emerged as a viable approach to address the challenges associated with continuous or quasicontinuous plasma processes. To this end, the authors previously reported the quasiatomic layer etching of silicon nitride via sequential exposure to hydrogen and fluorinated plasma. The underlying premise was the surface modification via implantation of hydrogen ions into silicon nitride resulting in an anisotropic etch. In this paper, the authors will demonstrate that a similar enhancement in reactivity of silicon nitride can also be attained via diffusion of hydrogen atoms into silicon nitride with the resultant etch being isotropic. These results confirm the realization of self-limiting etch of silicon nitride with tunable directionality. Selectivity to oxide is >100 and damage to underlying silicon can be minimized by optimizing the flux of atomic fluorine during the exposure to fluorinated plasma. Thus, hydrogen plasma step controls the directionality while fluorinated plasma step determines the selectivity to oxide and underlying silicon.

Atomic layer etching of silicon nitride using cyclic process with hydrofluorocarbon chemistry

In this study, atomic layer etching (ALE) of silicon nitride (SiN) using a cyclic process with monofluoromethane chemistry was investigated. Results show that an appropriate desorption time must be chosen at a specific adsorption time to achieve SiN ALE. The results also show that the infinite selectivity of SiN over Si can be achieved using the cycle process. To further understand this behavior, the adsorption and desorption effects were also studied. The results revealed a mechanism to obtain a high Si selectivity and a dominant factor that causes the Si loss. To further understand the ALE capability, we studied and compared the etched profiles and resulting surface roughness obtained by both a conventional process and an ALE process. The results show that the ALE process can achieve a high Si selectivity and a non-detectable level of Si surface damage, compared with a conventional continuous etching process.

Etching and Chemical Control of the Silicon Nitride Surface.

Silicon nitride is used for many technological applications, but a quantitative knowledge of its surface chemistry is still lacking. Native oxynitride at the surface is generally removed using fluorinated etchants, but the chemical composition of surfaces still needs to be determined. In this work, the thinning (etching efficiency) of the layers after treatments in HF and NH4F solutions has been followed by using spectroscopic ellipsometry. A quantitative estimation of the chemical bonds found on the surface is obtained by a combination of infrared absorption spectroscopy in ATR mode, X-ray photoelectron spectroscopy, and colorimetry. Si-F bonds are the majority species present at the surface after silicon nitride etching; some Si-OH and a few Si-NHx bonds are also present. No Si-H bonds are present, an unfavorable feature for surface functionalization in view of the interest of such mildly reactive groups for achieving stable covalent grafting. Mechanisms are described to support the experimental results, and two methods are proposed for generating surface SiH species: enriching the material in silicon, or submitting the etched surface to a H2 plasma treatment.

Impact of Extended Contact Cofiring on Multicrystalline Silicon Solar Cell Parameters

During the temperature spike of the contact cofiring step in a solar cell process, it has been shown that the concentration of lifetime-killer dissolved metallic impurities increases, while adding an annealing after the spike getters most of the dissolved impurities toward the phosphorus emitter, where they are less detrimental. The contact cofiring temperature profile, including the after-spike annealing, has been called extended contact cofiring, and it has also been proposed as a means to decrease the emitter saturation current density of highly doped emitters, thus benefiting a wide range of materials in terms of detrimental impurity content. The aim of the present work is to determine the effect of performing this additional annealing on contact quality and solar cell performance, looking for an optimal temperature profile for reduction of bulk and emitter recombination without affecting contact quality. It presents the effect of the extended cofiring step on fill factor, series resistance, and contact resistance of solar cells manufactured with different extended cofiring temperature profiles. Fill factor decreases when extended cofiring is performed. Series resistance and contact resistance increase during annealing, and this happens more dramatically when the temperature peak is decreased. Scanning electron microscopic images show silver crystallites in contact with silver bulk before the annealing that allow a direct current path, and silver crystallites totally surrounded by glass layer ( $>$ 100 nm thick) after annealing. Glass layer redistribution and thickening at low temperatures at the semiconductor–metal interface can be related to the series resistance increase. Degradation of series resistance during the temperature spike, when it is below the optimum one, can also be attributed to an incomplete silicon nitride etching and silver crystallite formation. To make full use of the beneficial effects of annealing, screen-printing metallic paste development supporting lower temperatures without a thick glass layer growth is needed.

Electron beam generated plasmas: Characteristics and etching of silicon nitride

The Naval Research Laboratory (NRL) has developed a processing system based on an electron beam-generated plasma, where unlike conventional discharges produced by electric fields (DC, RF, microwave, etc.), ionization is driven by a high-energy (~keV) electron beam. The resulting plasmas are characterized by large electron densities (1010–1011cm−3) and low electron temperatures (0.3–1.0eV). Accordingly, a large flux of ions can be delivered to substrate surfaces with kinetic energies of only a few eV, a feature that can be attractive to processing applications that require low damage and atomic layer precision. This work describes the salient features of these plasmas produced in mixtures of argon and sulfur hexafluoride (SF6) and their use in silicon nitride etching, with particular attention paid to developing processing parameters relevant to atomic layer processing.

Quasi-atomic layer etching of silicon nitride

Atomic layer etching (ALE) is a promising technique that can solve the challenges associated with continuous or pulsed plasma processes—trade-offs between selectivity, profile, and aspect ratio dependent etching. Compared to silicon, oxide, and other materials, atomic layer etching of silicon nitride has not been extensively reported. In this paper, the authors demonstrate the self-limited etching of silicon nitride in a commercial plasma etch chamber. The process discussed in this paper consists of two sequential steps—surface modification in hydrogen plasma followed by the removal of modified layers in fluorinated plasma. In addition to the ALE characteristics, the authors also demonstrate that the process is anisotropic and the selectivity to oxide is >100. Although the saturated etch rate of one monolayer per cycle could not be attained, self-limited etching of silicon nitride still enables us to incorporate the benefits of atomic layer etching such as an absence of isodense bias and an extremely high selectivity to oxide into practical etch applications.

ProTEK PSB as Biotechnology Photosensitive Protection Mask on 3C-SiC-on-Si in MEMS Sensor

This project presents the fabrication of MEMS employing a cubic silicon carbide (3C- SiC) on silicon wafer using newly developed ProTEK PSB as biotechnology photosensitive protection mask. This new biotechnology can reduce the number of processes and simplify the process flow with minimal impact on overall undercut performance. The 680 pm thick wafer is back-etched, leaving the 3C-SiC thin film with a thickness of 1.0 μm as the flexible diaphragm to detect pressure. The effect of the new coating of ProTEK PSB on different KOH solvents were investigated depending on various factors such as development time, final cure temperature and the thickness of the ProTEK PSB deposited layer. It is found that 6.174 μm thickness of ProTEK PSB offers some possibility of reducing the processing time compared to silicon nitride etch masks in KOH (55%wt, 80°C). The new ProTEK PSB biotechnology photosensitive protection mask indicates good stability and sustains its performance in different treatments under KOH and IPA for 8 hours. This work also revealed that the fabrication of MEMS sensors using the new biotechnology photosensitive protection mask provides a simple assembly approach and reduces manufacturing costs. The MEMS sensor can operate up to 500 °C as indicated under the sensitivity of 0.826 pF/MPa with nonlinearity and hysteresis of 0.61% and 3.13%, respectively.

Thermal cyclic etching of silicon nitride using formation and desorption of ammonium fluorosilicate

Novel selective cyclic etching of SiN over SiO2 via the formation and desorption of ammonium fluorosilicate was developed. The formation of ammonium fluorosilicate was observed using X-ray photoelectron spectroscopy after hydrofluorocarbon-based radical exposure. Etching of SiN was observed after ammonium fluorosilicate was removed by thermal annealing. Cyclic etching tests were carried out by repeated radical exposure and thermal annealing. The etching depth increased on increasing the number of cycles. It was found that the cyclic etching is self-limiting because the etching depth does not depend on the radical exposure time but on the number of cycles.

Silica Formation during Etching of Silicon Nitride in Phosphoric Acid

The etching of silicon nitride using phosphoric acid with silicon dioxide as a mask is an important process step used in the production of 3D NAND devices. This paper examines the theory of formation of a silica film onto the silicon dioxide surface during this etching step by performing a shell balance analysis of silica species in the etched out liquid volume of the 3D NAND structures. The method of moments is used to solve for the moments of the distribution of particle sizes, and this is used to solve for the potential energy barrier for silica particles to adhere to the silicon dioxide surface.

Selective Etching of Silicon Oxide versus Nitride with Low Oxide Etching Rate

This paper describes both aqueous and solvent-based formulations aimed at etching silicon oxide (SiOx) with etching rates (E/R) of the order of 10-20 A/min with selectivity greater than 5 with respect to silicon nitride (SiNx) . Diluted hydrofluoric acid (dHF) with very low pH was tried first but the selectivity was found to increase only with higher SiOx E/R. Solvent-based formulations derived from previous work also behaved in a similar way, however its SiOx E/R could be reduced by modifying the total fluoride concentration inside formulation. Finally, we found that low SiOx E/R could also be implemented in the diluted buffer-oxide etch (BOE) solution and the selectivity could be adjusted by addition of a specific surfactant at a very low concentration level.

Thin Layer Etching of Silicon Nitride: Comparison of Downstream Plasma, Liquid HF and Gaseous HF Processes for Selective Removal after Light Ion Implantation

For technology nodes beyond 14nm silicon nitride spacer etching has become a major challenge. Conventional plasma etching techniques based on CHF3/O2 cannot achieve thorough nitride removal on horizontal surfaces without inducing either CD loss or Si/SiGe source/drain recess. This leads to either gate leakage increase or poor raised source/drain epitaxy. To overcome atomic scale control issues faced with continuous plasma processes, several techniques aiming at achieving atomic layer etching or thin layer etching were recently described [1]. An original etching approach has been reported which consists in modifying the silicon nitride through H2 ion implantation by plasma (ICP or CCP) and then selectively removing the modified fraction of the layer thanks to chemical etching [2]. Layer modification depth is controlled thanks to plasma parameters (bias voltage and process time). This unconventional technique was demonstrated on 14nm FDSOI logic device and showed less than 1nm spacer CD loss, less than 0.6nm SiGe recess which enabled defect-free source/drain epitaxy [2]. Mechanisms for silicon nitride modifications and selective removal are discussed in this article by comparing downstream plasma, liquid-phase HF and gas-phase HF as removal techniques.

Metrology for High Selective Silicon Nitride Etch

This paper demonstrates a variety of metrology methods for high selective silicon nitride etch in different process baths. Capability of measuring full matrix components is also presented. For the measurement of H3PO4 and H2O, both NIR spectroscopy and conductivity methods work well. Si measurement in the etchant that contains an organo-silicon compound requires a new reagent development in comparison with the original reagent method developed for regular process contains inorganic Si only.

SiN etching characteristics of Ar/CH3F/O2 plasma and dependence on SiN film density

We evaluated the silicon nitride (SiN) etching characteristics of Ar/O2/hydrofluorocarbon plasma. Ar/CH3F/O2 plasma achieved a high etching selectivity of SiN to SiO2 by increasing the oxygen flow rate. We also evaluated the dependence of SiN etching characteristics on SiN film density. A low-density film deposited at a low temperature of 200 °C (by plasma-enhanced CVD, PECVD) showed an 8–20% lower etching rate of SiN than a high-density film deposited at a high temperature of 780 °C (by low-pressure CVD, LPCVD) when we had a low RF bias of 30 W. This PECVD film might move the competitive balance to oxidation from fluorination, reducing the SiN etching rate. However, when we have a high RF bias of more than 50 W, the SiN etching rate is 2–15% higher in the PECVD film than in the LPCVD film. The etching rate of SiN at various densities depends on the balance between oxidation and ion bombardment.

Silicon nitride and silicon etching by CH3F/O2 and CH3F/CO2 plasma beams

Silicon nitride (SiN, where Si:N ≠ 1:1) films low pressure-chemical vapor deposited on Si substrates, Si films on Ge on Si substrates, and p-Si samples were exposed to plasma beams emanating from CH3F/O2 or CH3F/CO2 inductively coupled plasmas. Conditions within the plasma beam source were maintained at power of 300 W (1.9 W/cm3), pressure of 10 mTorr, and total gas flow rate of 10 sccm. X-ray photoelectron spectroscopy was used to determine the thicknesses of Si/Ge in addition to hydrofluorocarbon polymer films formed at low %O2 or %CO2 addition on p-Si and SiN. Polymer film thickness decreased sharply as a function of increasing %O2 or %CO2 addition and dropped to monolayer thickness above the transition point (∼48% O2 or ∼75% CO2) at which the polymer etchants (O and F) number densities in the plasma increased abruptly. The C(1s) spectra for the polymer films deposited on p-Si substrates appeared similar to those on SiN. Spectroscopic ellipsometry was used to measure the thickness of SiN films etched using the CH3F/O2 and CH3F/CO2 plasma beams. SiN etching rates peaked near 50% O2 addition and 73% CO2 addition. Faster etching rates were measured in CH3F/CO2 than CH3F/O2 plasmas above 70% O2 or CO2 addition. The etching of Si stopped after a loss of ∼3 nm, regardless of beam exposure time and %O2 or %CO2 addition, apparently due to plasma assisted oxidation of Si. An additional GeOxFy peak was observed at 32.5 eV in the Ge(3d) region, suggesting deep penetration of F into Si, under the conditions investigated.

Surface etching, chemical modification and characterization of silicon nitride and silicon oxide—selective functionalization of Si3N4 and SiO2

The ability to selectively chemically functionalize silicon nitride (Si3N4) or silicon dioxide (SiO2) surfaces after cleaning would open interesting technological applications. In order to achieve this goal, the chemical composition of surfaces needs to be carefully characterized so that target chemical reactions can proceed on only one surface at a time. While wet-chemically cleaned silicon dioxide surfaces have been shown to be terminated with surficial Si–OH sites, chemical composition of the HF-etched silicon nitride surfaces is more controversial. In this work, we removed the native oxide under various aqueous HF-etching conditions and studied the chemical nature of the resulting Si3N4 surfaces using infrared absorption spectroscopy (IRAS), x-ray photoelectron spectroscopy (XPS), low energy ion scattering (LEIS), and contact angle measurements. We find that HF-etched silicon nitride surfaces are terminated by surficial Si–F and Si–OH bonds, with slightly subsurface Si–OH, Si–O–Si, and Si–NH2 groups. The concentration of surficial Si–F sites is not dependent on HF concentration, but the distribution of oxygen and Si–NH2 displays a weak dependence. The Si–OH groups of the etched nitride surface are shown to react in a similar manner to the Si–OH sites on SiO2, and therefore no selectivity was found. Chemical selectivity was, however, demonstrated by first reacting the –NH2 groups on the etched nitride surface with aldehyde molecules, which do not react with the Si–OH sites on a SiO2 surface, and then using trichloro-organosilanes for selective reaction only on the SiO2 surface (no reactivity on the aldehyde-terminated Si3N4 surface).

Prediction of plasma-induced damage distribution during silicon nitride etching using advanced three-dimensional voxel model

The authors modeled SiN film etching with hydrofluorocarbon (CHxFy/Ar/O2) plasma considering physical (ion bombardment) and chemical reactions in detail, including the reactivity of radicals (C, F, O, N, and H), the area ratio of Si dangling bonds, the outflux of N and H, the dependence of the H/N ratio on the polymer layer, and generation of by-products (HCN, C2N2, NH, HF, OH, and CH, in addition to CO, CF2, SiF2, and SiF4) as ion assistance process parameters for the first time. The model was consistent with the measured C-F polymer layer thickness, etch rate, and selectivity dependence on process variation for SiN, SiO2, and Si film etching. To analyze the three-dimensional (3D) damage distribution affected by the etched profile, the authors developed an advanced 3D voxel model that can predict the time-evolution of the etched profile and damage distribution. The model includes some new concepts for gas transportation in the pattern using a fluid model and the property of voxels called “smart voxels,” which contain details of the history of the etching situation. Using this 3D model, the authors demonstrated metal–oxide–semiconductor field-effect transistor SiN side-wall etching that consisted of the main-etch step with CF4/Ar/O2 plasma and an over-etch step with CH3F/Ar/O2 plasma under the assumption of a realistic process and pattern size. A large amount of Si damage induced by irradiated hydrogen occurred in the source/drain region, a Si recess depth of 5 nm was generated, and the dislocated Si was distributed in a 10 nm deeper region than the Si recess, which was consistent with experimental data for a capacitively coupled plasma. An especially large amount of Si damage was also found at the bottom edge region of the metal–oxide–semiconductor field-effect transistors. Furthermore, our simulation results for bulk fin-type field-effect transistor side-wall etching showed that the Si fin (source/drain region) was directly damaged by high energy hydrogen and had local variations in the damage distribution, which may lead to a shift in the threshold voltage and the off-state leakage current. Therefore, side-wall etching and ion implantation processes must be carefully designed by considering the Si damage distribution to achieve low damage and high transistor performance for complementary metal–oxide–semiconductor devices.

Selective Silicon Nitride Etch with Hot Diluted HF– an Alternative to Orthophosphoric Acid

Orthophosphoric acid is the worldwide standard chemical to quickly and selectively etch thick silicon nitride films towards silicon oxide. Along the semiconductors node evolution, new demands have arisen to etch few nanometers thick SiN films, with much better defectivity than H3PO4. Several alternatives have been developed during the past few years. Among them, a hot very diluted HF process was developed in the early 2000’s. This paper deals with several applications where significant benefits are demonstrated compared with H3PO4: first a Stress Proximity Technic successfully adopted into production mode, secondly a SiN films patterning thanks to a softmask. Although this process benefits from high selectivity, low cost of ownership, good defectivity, its within wafer uniformity still remains poor due to the actual hardware.

Etching of Silicon Nitride in 3D NAND Structures

3D NAND structures present a unique difficulty in semiconductor device manufacturing. One method of production consists of cylindrical structures made of alternating layers of silicon dioxide (SiO2) and silicon nitride (SiN) with a core of SiO2. As part of the device manufacturing process the SiN is etched away, leaving the SiO2 core with disc-shaped SiO2 fins. Due to material selectivity requirements of etching only the SiN while leaving the SiO2 unchanged, the process of choice is often immersion in a high-concentration hot phosphoric acid (H3PO4) bath with a silica additive to inhibit SiO2 etching, which with proper tuning can have selectivity of greater than 100:1 for etching SiN:SiO2. Like all wet etch processes, uniformity of the process is a constant concern. One of our goals in this paper is to show how we use experimental measurements and simulations to better understand what parameters have the most effect on the process, and how we can use that knowledge to improve the process. Experimentally we have measured the etch rate of blanket SiN and SiO2 wafers. We fit the etch rate data to Arrhenius models to quantify the etch rate of SiN and SiO2 films. Simulations of the etch process on both blanket wafers and patterned wafers showed that the etch rate is the same and doesn’t depend on feature geometry. In this paper we propose a simple chemical reaction and diffusion mechanism that explains the experimental observations of the etched structures. The uniformity of the SiN etching between the top and the bottom of the 3D NAND stacks indicates that the reaction rate is much slower than the rate of diffusion of reactants and products into and out of the structure, so the etching is a reaction-controlled mechanism. This indicates within-wafer uniformity and wafer-to-wafer uniformity variations as being primarily due to differences of temperature within the bath. We also conducted simulations of the etching of the SiN in the 3D NAND structure and the liquid flow in the bath to model and explain this mechanism. In these simulations we varied the rate of the surface reaction of H3PO4 etching SiN, and showed that for a fast reaction rate that the structure would etch from the top to the bottom as the overall reaction rate become diffusion limited, while for a slow reaction rate the entire structure would etch uniformly, showing it to be a reaction limited process. Another issue with SiN etching in an H3PO4 bath is that the etch rate of SiO2 depends highly on the concentration of silica, in fact the bath is generally pre-seeded with silica in order to achieve a lower SiO2 etch rate, though if above a critical concentration deposition is known to occur. Based on a study of silica chemistry, it may be possible for silica deposition to occur even when below the critical concentration. This would be a film that would grow on a SiO2 surface but would later dissolve back into solution. We propose a mechanism that explains the formation and later disappearance of the growth film on the SiO2 surface as a result of the etching of the SiN and the formation of silica byproducts into a sol/gel network. Sol/gels have the unique property of their ability to form in an area of locally high flux, and then later dissolve over a much longer time scale. The difference in forward and backward reaction rates of the sol/gel film formation and disillusion, respectively, are such that the system is never in equilibrium. Thus, even though all the silica can dissolve in the phosphoric acid at equilibrium, the silica formed from the SiN etching forms into a sol/gel polymer network that only slowly dissolves after SiN etching has stopped. We discuss the implications of this sol/gel oxide film for further process improvement. With better theoretical understanding of the SiN etching and possible silica sol/gel formation and dissolution process, we now have tools to better optimize the phosphoric acid bath, improving both etching uniformity and necessary process time. Figure 1

Selective Silicon Nitride Etch with Hot Diluted HF– an Alternative to Orthophosphoric Acid

Orthophosphoric acid is the worldwide standard chemistry to selectively etch silicon nitride towards silicon oxide [1]. Several alternatives have arisen since few years. Among them, a hot very diluted HF process has been developed in the early 2000’s [2]. This paper deals with its applications and adoption in production. Until the 45nm node, CMOS transistors manufacturing only one or two silicon nitride etch operations were use, namely to define the Shallow Trench Isolation [3]. Latest nodes require more and more SiN etch operations either to define hardmasks or to generate localized stress: SPT (Stress Proximity Technic) [4] [5] or SMT (Stress Memory Technic) [6]. H3PO4 benefits from tremendous etch selectivity towards silicon oxide. Nonetheless it still remains in reclaim immersion batch tool with drawbacks: particles and metals intra or inter batch cross contamination. Various alternatives are under development: chemical formulation [7], single wafer approach [8] or plasma solutions [9]. There’s still a long way to overpass cross contamination concerns, and compete with high productive, low cost of ownership H3PO4 wet benches. Last alternative relies on hot very diluted HF. It has never really been adopted by the industry due to relatively low SiN etch rates. It perfectly suits etching application of small SiN removal amount. Two applications are hereby described. First, a SPT technic in a 28nm node is considered. A comparison between two chemicals is made to remove the PECVD SiN spacer (figure 1). Its high etch rate of 9nm/min for the 85% H3PO4 wet bench at 165°C leads to short process (110s), poorly uniform. Moreover the SiN / SiO2 selectivity is only 30:1, and phosphoric acid is incompatible with highly As doped silicon films (figures 1 b) & 2). Si Gate and active areas are both corroded. Indeed, the transistor architecture makes the doped gates quite at risk with thin silicon oxide protection. Whereas H3PO4 has very poor process window, the hot very diluted HF in a spray batch tool enables better selectivity towards silicon oxide (60:1) and reduced corrosion of doped silicon. Moreover, excellent defectivity is obtained on silicon oxide surfaces (figure 3) making this process industrial. Second described application relies on SiN patterning by wet etching. Phosphoric acid isn’t used for such application due to reclaim issues, and swelling resist with high temperature. Applications exist with low temperature H3PO4 formulations [10] but decreases significantly the etch rate. Fresh, hot very diluted HF enables LPCVD SiN patterning without any resist lift off. The process window is large and without any resist optimization (248nm DUV resist 235nm thick). Last optimization would be the within wafer uniformity (15% 3 sigma) (figure 5). conclusion: Hot diluted HF is proposed as an alternative to H3PO4 for thin SiN film etching with or without resist presence. Its benefits are: fresh chemical use, low cross contamination risks, good defectivity, high compatibility with resist.