Silicon flower structures by maskless plasma etching

In semiconductor manufacturing, black silicon (bSi) has traditionally been considered as a sign of unsuccessful etching. However, after more careful consideration, many of its properties have turned out to be so superior that its integration into devices has become increasingly attractive. In devices where bSi covers the whole wafer surface, such as solar cells, the integration is already rather mature and different bSi fabrication technologies have been studied extensively. Regarding the integration into devices where bSi should cover only small selected areas, existing research focuses on device properties with one specific bSi fabrication method. Here, we fabricate bSi patterns with varying dimensions ranging from millimeters to micrometers using three common bSi fabrication techniques, i.e., plasma etching, metal-assisted chemical etching (MACE) and femtosecond-laser etching, and study the corresponding fabrication characteristics and resulting material properties. Our results show that plasma etching is the most suitable method in the case of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> -scale devices, while MACE reaches surprisingly almost the same performance. Femtosecond-laser has potential due to its maskless nature and capability for hyperdoping, however, in this study its moderate accuracy, large silicon consumption and spreading of the etching damage outside the bSi region leave room for improvement.

In the present work, we report, on the exceptionally high absorptivity of Black Silicon (BSi) in the spectral range of thermal radiation, which can be instrumental for various thermal radiation related applications. Having fabricated two wafers of BSi having n-type low and high doping, we have found experimentally that for highly doped BSi, a high absorptivity is observed till 15 µm which has also been compared with similarly doped Flat Si (FSi) samples. However, beyond 15 µm, the absorptivity of highly doped BSi sample decreases. Subsequent processing of SEM images reveals that these noteworthy radiative properties can probably be attributed to particular morphological features of heavily doped BSi at the nanoscale. These features are quantified through statistical image processing. Reported results pave the way to highly integrated and effective infrared sources using Black Silicon.

This article discusses a method for forming black silicon using plasma etching at a sample temperature range from -20 °C to +20 °C in a mixture of oxygen and sulfur hexafluoride. The surface morphology of the resulting structures, the autocorrelation function of surface features, and reflectivity were studied depending on the process parameters-the composition of the plasma mixture, temperature and other discharge parameters (radical concentrations). The relationship between these parameters and the concentrations of oxygen and fluorine radicals in plasma is shown. A novel approach has been studied to reduce the reflectance using conformal bilayer dielectric coatings deposited by atomic layer deposition. The reflectivity of the resulting black silicon was studied in a wide spectral range from 400 to 900 nm. As a result of the research, technologies for creating black silicon on silicon wafers with a diameter of 200 mm have been proposed, and the structure formation process takes no more than 5 min. The resulting structures are an example of the self-formation of nanostructures due to anisotropic etching in a gas discharge plasma. This material has high mechanical, chemical and thermal stability and can be used as an antireflective coating, in structures requiring a developed surface-photovoltaics, supercapacitors, catalysts, and antibacterial surfaces.

As a widely used semiconductor material, silicon has been extensively used in many areas, such as photodiode, photodetector, and photovoltaic devices. However, the high surface reflectance and large bandgap of traditional bulk silicon restrict the full use of the spectrum. To solve this problem, many methods have been developed. Among them, the surface nanostructured silicon, namely black silicon, is the most efficient and widely used. Due to its high absorption in the wide range from UV-visible to infrared, black silicon is very attractive for using as sensitive layer of photodiodes, photodetector, solar cells, field emission, luminescence, and other photoelectric devices. Intensive study has been performed to understand the enhanced absorption of black silicon as well as the response extended to infrared spectrum range. In this paper, the application of black silicon is systematically reviewed. The limitations and challenges of black silicon material are also discussed. This article will provide a meaningful introduction to black silicon and its unique properties.

An alternative approach for femtosecond laser induced black silicon in ambient air

Light scattering from black silicon surfaces and its benefits for encapsulated solar cells

We present a scalable strategy for fabricating super-liquid-repellent surfaces by depositing polytetrafluoroethylene (PTFE) onto black silicon (bSi) substrates. Needle-like microstructures were initially fabricated on a Si wafer via fluorine plasma etching using plasma-based ion implantation and deposition (PBII&D). Subsequent thermal evaporation of PTFE formed overhanging nanospikes on the needle-like microstructures of bSi, resulting in a composite solid-air interface characteristic of the Cassie-Baxter state. The engineered surfaces exhibited outstanding repellency to various liquids, including water (θ* = 172°, θroll-off = 4°), diethylene glycol (θ* = 168°, θroll-off = 4.4°), hexadecane, and commercial ink for large-format inkjet printing. To extend this functionality to diverse substrates, we employed a supplementary approach using Si-based amorphous films, such as a-C:H:Si:O films, deposited using hexamethyldisiloxane as a precursor gas. Needle-like microstructures were successfully replicated using a-C:H:Si:O films via plasma etching under conditions identical to those used for bSi substrates. PTFE deposition on these replicated structures achieved comparable liquid-repellent performance, demonstrating the feasibility of integrating hierarchical bSi-inspired morphologies on diverse materials. The combined use of scalable techniques, such as PBII&D and thermal evaporation, enables large-area fabrication of robust liquid-repellent surfaces for industrial applications.

In this paper, the optical properties of black silicon have been studied. The black silicon samples were fabricated by alkaline etching and metal assisted etching. The micro-columns and nanopores on the silicon surface were obtained in KOH and Au-induced HF/H2O2 solution, respectively. The height and diameter of micro-columns prepared by KOH etching is about 470 nm and 2 μm. In the Au-induced HF/H2O2 etching, the metallic nuclei behave as a cathode and their surrounding area acts as an anode, resulting in nanopores with diameters ranging from 80 to 120 nm. These microstructures formed in the etching process directly affect the optical properties of black silicon such as reflectance, transmittance and absorptance. According to the measurement of integrating sphere detector, the absorptance of the black silicon produced by wet etching remains roughly 90% from 250 to 1,000 nm wavelength, which is almost 150% of the absorptance of conventional silicon. However, the reflectance of black silicon is less than 13% and the transmittance is less than 4%.

Silicon is widely used in semiconductor industry but has poor performance in near-infrared photoelectronic devices because of its high reflectance and band gap limit. In this study, two-step process, deep reactive ion etching (DRIE) method combined with plasma immersion ion implantation (PIII), are used to fabricate microstructured black silicon on the surface of C-Si. These improved surfaces doped with sulfur elements realize a narrower band gap and an enhancement of light absorptance, especially in the near-infrared range (800 to 2000 nm). Meanwhile, the maximum light absorptance increases significantly up to 83%. A Si-PIN photoelectronic detector with microstructured black silicon at the back surface exhibits remarkable device performance, leading to a responsivity of 0.53 A/W at 1060 nm. This novel microstructured black silicon, combining narrow band gap characteristic, could have a potential application in near-infrared photoelectronic detection.

As semiconductor devices are highly integrated, etching control is much more difficult in semiconductor industry. Plasma etching has better performance than wet etching especially in small open area etching. In semiconductor manufacturing industry, the optical emission spectroscopy (OES) is widely used to collect data from plasma chamber. The enormous OES data need to be transformed for accutate endpoint detection. There are some research results regarding endpoint detection in plasma etching using various methods such as Principal Component Analysis (PCA), Partial Least Squares (PLS), etc. In this paper a new approach is proposed for endpoint detection of small open area wafers in plasma etching. The new approach utilizes a Fast Fourier Transform (FFT), which is an efficient algorithm to detect frequency changes in signal, and this property is applied to OES data to detect endpoint in etching process. By applying FFT, noise is reduced compared to PCA data. The data after FFT is used to detect endpoint using Support Vector Machine (SVM). The combination of FFT and SVM performs excellent in terms of endpoint detection, and the performance of proposed FFT/SVM algorithm is compared to the performance of PCA/SVM algorithm.

Optimization of etching time for broadband absorption enhancement in black silicon fabricated by one-step electroless silver-assisted wet chemical etching

Plasma etching, which is expected to play an important role in the manufacture of semiconductor and other devices requiring fine–line lithography, involves using a glow discharge to generate chemically reactive species from relatively inert molecular gases.1 These reactive species combine chemically with certain solid materials to form volatile compounds which are removed by the vacuum pumping system. Although the general concept is relatively simple, the complexities of the glow discharge itself and of the associated parameter space have impeded the development of a detailed understanding of the chemical reactions involved in the process, which in turn has impeded the implementation of plasma etching in device manufacture.

Commercial quadrupole mass spectrometer (QMS) residual gas analyzers became available in the late 1960s and have been popular in R&amp;D laboratories, but have found limited use in semiconductor manufacturing. To sample at pressures above 10−5 Torr with ppm sensitivity or better (relative to the total process pressure), differential pumping is usually required. The newly available, small, high-pressure QMS sensors can operate as high as 10–20 mTorr without differential pumping, but provide somewhat lower mass resolution and partial pressure sensitivity than a standard QMS. Applications in semiconductor manufacturing include equipment monitoring, process monitoring, and effluent analysis. Equipment monitoring can include qualification after preventative maintenance, rate-of-rise tests, and leak identification and detection. Usually the burning question is, Why won’t the vacuum chamber pump down? Other uses that are not usually considered include the qualification of replaceable parts: sputter cathodes, electrodes, lamps, shields, etc. In process monitoring, the key question is, Is this process running normally? A manufacturing monitor can be useful simply by providing a comparison between a well-behaved high-yield process and a marginal or failing process. Examples are given for physical vapor deposition (sputtering) processes, chemical vapor deposition, and plasma etching. The effluent from chemical vapor deposition and plasma etch processes can be analyzed to measure the efficiency of process gas utilization or to monitor the efficacy of abatement methods used for the removal of global warming gases.

With the rising demand for higher quantities and quality of semiconductors, refining production processes is essential. Plasma etching, a key step in semiconductor manufacturing, is valued for its precision and speed but is also vulnerable to plasma arcing - an electrical discharge that can cause significant damage to wafers and equipment. Rapid and reliable detection of arcing incidents is critical for maintaining yield and minimizing downtime. Traditional detection methods, such as static thresholds applied to Radio Frequency signals, often struggle with non-linear signal characteristics and ambiguous edge cases, resulting in false positives or missed events. To address these challenges, this paper introduces a novel, real-time, configurable statistical anomaly detection framework specifically designed for arcing incidents in plasma etching. The system combines dynamic feature monitoring with a multi-feature validation approach, reducing false positives and improving detection accuracy. In addition, a proof-of-concept severity scoring system is introduced to provide tunable, heuristic-based scoring of detected events, enabling engineers to assess potential impact. Evaluated under log-level labeling constraints using proprietary etching logs, the proposed framework exhibits promising detection performance relative to naive threshold-based approaches and representative machine learning baselines evaluated for comparison, including LSTM, one-class SVM, and Isolation Forest, while maintaining compatibility with real-time process constraints. The system’s modular design further allows for potential adaptation across different etching configurations, offering a practical and efficient proof-of-concept framework for real-time process monitoring in semiconductor manufacturing.

Virtual metrology (VM) is attracting much interest from semiconductor manufacturers because of its potential advantages for quality control. Plasma etching equipment with state-of-the-art plasma sensors are attractive for implementing VM. However, the plasma sensors requiring physical understanding make it difficult to select input parameters for VM. In addition, those sensors with high sensitivity frequently cause several issues in terms of VM performance. This paper will address plasma sensor issues in implementing a robust VM, where self-excited electron resonance spectroscopy, optical emission spectroscopy, and VI-probe are utilized for critical dimension prediction in a plasma etching process. An optimum sensor selection technique which can give insight into effectiveness of plasma sensors is introduced. In this technique, a numerical criterion, integrated squared response, is proposed for effective selection of important sensors for particular manipulated variables. Sensor data shift across equipment preventive maintenance (PM) and its impact on VM performance are also addressed, where a recursive data centering technique is introduced to handle PM-to-PM sensor data drift in a cost-effective way. The application of the technique introduced in this paper is shown to be effective in dynamic random access memory manufacturing. Hopefully, these results will encourage further implementation of robust virtual metrology in plasma etching for semiconductor manufacturing.