Reduction of EUV resist damage by neutral beam etching

Even though EUV lithography has the advantage of implenting a finer pattern compared to ArF immersion lithography due to the use of 13.5 nm instead of 193 nm as the wavelengh of the light source, due to the low energy of EUV light source, EUV resist has a thinner thickness than conventional ArF resist. EUV resist having such a thin thickness is more vulnerable to radiation damage received during the etching because of its low etch resistance and also tends to have a problem of low etch selectivity. In this study, the radiation damage to EUV resist during etching of hardmask materials such as Si3N4, SiO2, etc. using CF4 gas was compared between neutral beam etching (NBE) and ion beam etching (IBE). When NBE was used, after the etching of 20 nm thick EUV resist, the line edge roughness (LER) increase and the critical dimension (CD) change of EUV resist were reduced by ~ 1/3 and ~ 1/2, respectively, compared to those by IBE. Also, at that EUV etch depth, the RMS(root mean square) surface roughness value of EUV resist etched by NBE was ~2/3 compared to that by IBE on the average. It was also confirmed that the etching selectivity between SiO2, Si3N4, etc. and EUV resist was higher for NBE compared to IBE. The less damage to the EUV resist and the higher etch selectivity of materials such as Si3N4 and SiO2 over EUV resist for NBE compared to IBE are believed to be related to the no potential energy released by the neutralization of the ions during the etching for NBE.

Research on Trench Etching and Photolithography Process of SiC Trench MOSFET

In this paper, the development of trench etching process and photolithography process for 6-inch 4H-SiC trench-type power MOSFET devices is mainly studied. Among them, the etching process successfully solved the anisotropy of dry etching of SiC, the different etching rates of different crystal planes, the difficulty of controlling the angle of the trench sidewall, and the easy formation of micro-trenches at the corners, etc. Successfully realized trenches with etch depth greater than 1.2um and sidewall angle greater than 90° in SiC. Subsequently, the trench was filled with SiO2 to achieve no holes in the trench after filling, and then the photolithography process was studied. Photolithography process is resolved at the trench coating, exposing and developing the non-uniformity problem, achieve a full and uniform coating, self-aligned trench overlay and the overlay accuracy of less than 0.1um, and there is no residue of photoresist in the groove after development. This article uses scanning electron microscope (SEM) to measure the morphology of the trench after etching and photolithography to characterize the experimental results, and the results meet the process requirements. The successful development of this process will facilitate the research and development of deeper trench-type power MOSFET devices.

Synthesis of highly efficient multilayer dielectric diffraction gratings for spectral combining of laser beams

Статья посвящена синтезу многослойных диэлектрических отражательных дифракционных решеток, с высокой эффективностью обеспечивающих спектральное сложение пучков с различной длиной волны в заданном дифракционном порядке. Приводятся результаты решения задачи синтеза многослойных диэлектрических дифракционных решеток, обеспечивающих спектральное сложение в первом или минус первом порядке дифракции. Кроме того, решается задача синтеза для таких решеток с учетом возможных технологических ограничений на высоту профиля (глубину травления). Решение задачи синтеза проводится путем минимизации зависящего от параметров решетки целевого функционала методом Нелдера-Мида. Решение прямой задачи на каждом шаге минимизации осуществляется при помощи комбинации неполного метода Галеркина и метода матриц рассеяния. The paper is devoted to the synthesis of multilayer dielectric reflection diffraction gratings providing high-efficiency spectral combining of the beams with different wavelengths in a given diffraction order. The results are presented for solving the synthesis problems for multilayer dielectric diffraction gratings providing spectral combining in the first or minus first diffraction order. Besides, the synthesis problem for such gratings is solved with account taken of possible technological constraints imposed by the height of the grating profile (etch depth). The solution of the synthesis problem is obtained by means of Nelder-Mead minimization of the merit function depending on the grating parameters. At each minimization step the direct problem is solved using a combination of the incomplete Galerkin method and scattering matrix method.

Silicon Carbide Wafer Machining by Using a Single Filament Plasma at Atmospheric Pressure

SiC wafers were etched using a filament plasma of He:NF3:O2 (helium:nitrogen trifluoride:oxygen) mixed gas at atmospheric pressure. When 0.5–2 sccm of NF3 was mixed to 2 slm of He filament plasma, the etch depth and etch rate increased, but there was little change in the etch width as the NF3 mixing amount increased. The increment of the NF3 mixing also suppressed the surface roughening of plasma etching. The addition of O2 to the He-NF3 filament plasma slightly increased the SiC wafer etch rate. When the NF3 mixing amount was 2 sccm, the roughness of the etched surface increased sharply by O2 addition. On the contrary, the NF3 mixing amount was 1 sccm; the addition of O2 reduced the roughness more than that of the pristine. The roughness of the pristine SiC wafer specimens is in the range of Ra 0.7–0.8 nm. After 30 min of etching on a 6 mm by 6 mm square area, the roughness of the etched surface reduced to Ra 0.587 nm, while the etch rate was 2.74 μm/h with a He:NF3:O2 of 2:1:3 (slm:sccm:sccm) filament plasma and 3 mm/s speed of raster scan etch of the optimized roughening suppression etching recipe.

Study of metal-assisted chemical etching of silicon as an alternative to dry etching for the development of vertical comb-drives

Metal-assisted chemical etching (MaCEtch) has recently emerged as a promising technique to etch anisotropic nano- and microstructures in silicon by metal catalysts. It is an economical wet chemical etching method, which can be a good alternative to deep-reactive ion etching (DRIE) process in terms of verticality and etch depth. In the present study, gold is used as a metal catalyst and deposited using physical vapour deposition. It has already been demonstrated that (100) p-type Si wafer can be etched with vertical and smooth side walls. Effects of varying concentrations of etchant constituents and various other parameters, that is, porosity of deposited Au, surface contaminants, oxide formation, metal catalyst, etching time, role of surface tension of additives on the etch depth and surface defects are studied and discussed in detail. By increasing the hydrofluoric acid (HF) concentration from 7.5 M to 10 M, lateral etching is reduced and the microstructure’s width is increased from 17 µm to 18 µm. Porous defects are suppressed by decreasing the hydrogen peroxide (H2O2) concentration from 1.5 M to 1 M. On increasing the etching time from 30 min to 60 min, the microstructures are over-etched laterally. Smoother side walls are fabricated by using the low-surface-tension additive ethanol. The maximum etch depth of 2.6 µm is achieved for Au catalyst in 30 min. The results are encouraging and useful for the development of vertical comb-drives and Micro-Electro-Mechanical Systems (MEMS).

Development of Virtual Metrology Using Plasma Information Variables to Predict Si Etch Profile Processed by SF6/O2/Ar Capacitively Coupled Plasma

In the semiconductor etch process, as the critical dimension (CD) decreases and the difficulty of the process control increases, in-situ and real-time etch profile monitoring becomes important. It leads to the development of virtual metrology (VM) technology, one of the measurement and inspection (MI) technology that predicts the etch profile during the process. Recently, VM to predict the etch depth using plasma information (PI) variables and the etch process data based on the statistical regression method had been developed and demonstrated high performance. In this study, VM using PI variables, named PI-VM, was extended to monitor the etch profile and investigated the role of PI variables and features of PI-VM. PI variables are obtained through analysis on optical emission spectrum data. The features in PI-VM are investigated in terms of plasma physics and etch kinetics. The PI-VM is developed to monitor the etch depth, bowing CD, etch depth times bowing CD (rectangular model), and etch area model (non-rectangular model). PI-VM for etch depth and bowing CD showed high prediction accuracy of R-square value (R2) 0.8 or higher. The rectangular and non-rectangular etch area model PI-VM showed prediction accuracy R2 of 0.78 and 0.49, respectively. The first trial of virtual metrology to monitor the etch profile will contribute to the development of the etch profile control technology.

Penscriptive Depth-Controlled Robotic Laser Osteotomy

Bone cutting in surgery is currently done using un-intelligent tools that depend on the proficiency of the surgeon to prevent damage to underlying critical structures. As one can imagine, damage isn’t always prevented. Iatrogenic damage to dura and sub-dural neural structures during osteotomical procedures such as a craniotomy can result in increased patient morbidity. This dissertation proposes the development of a robot-guided laser osteotome (bone cutter) with the use of inline optical coherence tomography (OCT) to precisely control the cutting depth in real-time. The all-fiber system design integrates a high peak-power pulsed Yb-doped fiber laser (1064nm) coupled directly into the sample arm of a swept-source OCT system (λc = 1310nm) with a fourth-order power disparity between the OCT system and fiber laser. Sub-millimeter accuracy was achieved in percussion drilling of phantom and porcine bone. Through the use of optical topographic imaging (OTI), this work presents a novel method for the surgeon to identify arbitrary trajectories for desired cuts. A surgical pencil is used to demarcate cutting trajectories for the robot to follow directly onto the boney surface. OTI imaging combined with a novel algorithm developed through this work allows the penscribed line to be isolated and translated into spatial attitude information for the robot to guide the end effector-mounted laser along. Sub-millimeter trajectory following accuracy was achieved. This work also demonstrates the first use of OCT in continuous, real-time refocusing of the optical end-effector in order to maintain cut quality. The focus of the laser was able to be maintained within the Rayleigh length of the focused Gaussian beam for linear feed rates up to 1mm/s at a 45◦ surface incline. Finally, optimization of bone ablation is explored in this dissertation. The use of graphite as a high-absorption topical chromophore and the use of nitrogen as an assist gas in the form of a coaxial jet are both analyzed to determine how to achieve the highest etch rate in bone. The results in this dissertation show that the topical application of graphite was able to significantly reduce the mean and variance of etching performance; an improvement by at least two orders of magnitude in the time to 0.5mm etch depth is demonstrated. It is also demonstrated that etch rate during ablation can be optimized for coaxial nitrogen flow (30SCFH out of a nozzle with 3mm output diameter); higher and lower flow rates showed slower etch rates. It is hypothesized that a system such as the one developed in this dissertation will increase the precision of bone cutting, decrease the amount of time needed to make cuts into sensitive structures and also address certain issues of unsuccessful uptake of lasers in modern medicine.

Penscriptive Depth-Controlled Robotic Laser Osteotomy

Bone cutting in surgery is currently done using un-intelligent tools that depend on the proficiency of the surgeon to prevent damage to underlying critical structures. As one can imagine, damage isn’t always prevented. Iatrogenic damage to dura and sub-dural neural structures during osteotomical procedures such as a craniotomy can result in increased patient morbidity. This dissertation proposes the development of a robot-guided laser osteotome (bone cutter) with the use of inline optical coherence tomography (OCT) to precisely control the cutting depth in real-time. The all-fiber system design integrates a high peak-power pulsed Yb-doped fiber laser (1064nm) coupled directly into the sample arm of a swept-source OCT system (λc = 1310nm) with a fourth-order power disparity between the OCT system and fiber laser. Sub-millimeter accuracy was achieved in percussion drilling of phantom and porcine bone. Through the use of optical topographic imaging (OTI), this work presents a novel method for the surgeon to identify arbitrary trajectories for desired cuts. A surgical pencil is used to demarcate cutting trajectories for the robot to follow directly onto the boney surface. OTI imaging combined with a novel algorithm developed through this work allows the penscribed line to be isolated and translated into spatial attitude information for the robot to guide the end effector-mounted laser along. Sub-millimeter trajectory following accuracy was achieved. This work also demonstrates the first use of OCT in continuous, real-time refocusing of the optical end-effector in order to maintain cut quality. The focus of the laser was able to be maintained within the Rayleigh length of the focused Gaussian beam for linear feed rates up to 1mm/s at a 45◦ surface incline. Finally, optimization of bone ablation is explored in this dissertation. The use of graphite as a high-absorption topical chromophore and the use of nitrogen as an assist gas in the form of a coaxial jet are both analyzed to determine how to achieve the highest etch rate in bone. The results in this dissertation show that the topical application of graphite was able to significantly reduce the mean and variance of etching performance; an improvement by at least two orders of magnitude in the time to 0.5mm etch depth is demonstrated. It is also demonstrated that etch rate during ablation can be optimized for coaxial nitrogen flow (30SCFH out of a nozzle with 3mm output diameter); higher and lower flow rates showed slower etch rates. It is hypothesized that a system such as the one developed in this dissertation will increase the precision of bone cutting, decrease the amount of time needed to make cuts into sensitive structures and also address certain issues of unsuccessful uptake of lasers in modern medicine.