High aspect ratio (HAR) silicon etch is reviewed, including commonly used terms, history, main applications, different technological methods, critical challenges, and main theories of the technologies. Chronologically, HAR silicon etch has been conducted using wet etch in solution, reactive ion etch (RIE) in low density plasma, single-step etch at cryogenic conditions in inductively coupled plasma (ICP) combined with RIE, time-multiplexed deep silicon etch in ICP-RIE configuration reactor, and single-step etch in high density plasma at room or near room temperature. Key specifications are HAR, high etch rate, good trench sidewall profile with smooth surface, low aspect ratio dependent etch, and low etch loading effects. Till now, time-multiplexed etch process is a popular industrial practice but the intrinsic scalloped profile of a time-multiplexed etch process, resulting from alternating between passivation and etch, poses a challenge. Previously, HAR silicon etch was an application associated primarily with microelectromechanical systems. In recent years, through-silicon-via (TSV) etch applications for three-dimensional integrated circuit stacking technology has spurred research and development of this enabling technology. This potential large scale application requires HAR etch with high and stable throughput, controllable profile and surface properties, and low costs.

High aspect ratio silicon etch: A review

On-chip optical resonators have the promise of revolutionizing numerous fields, including metrology and sensing; however, their optical losses have always lagged behind those of their larger discrete resonator counterparts based on crystalline materials and silica microtoroids. Silicon nitride (Si3N4) ring resonators open up capabilities for frequency comb generation, optical clocks, and high-precision sensing on an integrated platform. However, simultaneously achieving a high quality factor (Q) and high confinement in Si3N4 (critical for nonlinear processes, for example) remains a challenge. Here we show that addressing surface roughness enables overcoming the loss limitations and achieving high-confinement on-chip ring resonators with Q of 37 million for a ring of 2.5 μm width and 67 million for a ring of 10 μm width. We show a clear systematic path for achieving these high Qs, and these techniques can also be used to reduce losses in other material platforms independent of geometry. Furthermore, we demonstrate optical parametric oscillation using the 2.5 μm wide ring with sub-milliwatt pump powers and extract the loss limited by the material absorption in our films to be 0.13±0.05  dB/m, which corresponds to an absorption-limited Q of at least 170 million by comparing two resonators with different degrees of confinement. Our work provides a chip-scale platform for applications such as ultralow-power frequency comb generation, laser stabilization, and sideband-resolved optomechanics.

Ultra-low-loss on-chip resonators with sub-milliwatt parametric oscillation threshold

Atomic layer etching (ALE) is a technique for removing thin layers of material using sequential reaction steps that are self-limiting. ALE has been studied in the laboratory for more than 25 years. Today, it is being driven by the semiconductor industry as an alternative to continuous etching and is viewed as an essential counterpart to atomic layer deposition. As we enter the era of atomic-scale dimensions, there is need to unify the ALE field through increased effectiveness of collaboration between academia and industry, and to help enable the transition from lab to fab. With this in mind, this article provides defining criteria for ALE, along with clarification of some of the terminology and assumptions of this field. To increase understanding of the process, the mechanistic understanding is described for the silicon ALE case study, including the advantages of plasma-assisted processing. A historical overview spanning more than 25 years is provided for silicon, as well as ALE studies on oxides, III–V compounds, and other materials. Together, these processes encompass a variety of implementations, all following the same ALE principles. While the focus is on directional etching, isotropic ALE is also included. As part of this review, the authors also address the role of power pulsing as a predecessor to ALE and examine the outlook of ALE in the manufacturing of advanced semiconductor devices.

https://avs.scitation.org/doi/pdf/10.1116/1.4913379

Overview of atomic layer etching in the semiconductor industry

An object is to provide a method for manufacturing a semiconductor device, in which the number of photolithography steps can be reduced, the manufacturing process can be simplified, and manufacturing can be performed with high yield at low cost A method for manufacturing a semiconductor device includes the following steps: forming a semiconductor film; irradiating a laser beam by passing the laser beam through a photomask including a shield for shielding the laser beam; subliming a region which has been irradiated with the laser beam through a region in which the shield is not formed in the photomask in the semiconductor film; forming an island-shaped semiconductor film in such a way that a region which is not irradiated with the laser beam is not sublimed because it is a region in which the shield is formed in the photomask; forming a first electrode which is one of a source electrode and a drain electrode and a second electrode which is the other one of the source electrode and the drain electrode; forming a gate insulating film; and forming a gate electrode over the gate insulating film

Method for Manufacturing Semiconductor Device

Selective localization of active proteins to patterns or specific sites is important for development of biosensors, bioMEMS, tissue engineering, and basic proteomic research. We present a flexible technique for selectively patterning bioactive proteins with nanoscale resolution using nanoimprint lithography and fluoropolymer surface passivation, and exploiting the specificity of the biotin/streptavidin linkage. This technique achieves high throughput reproducible nanoscale protein patterns with high selectivity and retained biofunctionality, as demonstrated by interactions between patterned antibodies and their antigen.

Nanoscale protein patterning by imprint lithography

The mechanisms underlying selective etching of a SiO2 layer over a Si or Si3N4 underlayer, a process of vital importance to modern integrated circuit fabrication technology, has been studied. Selective etching of SiO2-to-Si3N4 in various inductively coupled fluorocarbon plasmas (CHF3, C2F6/C3F6, and C3F6/H2) was performed, and the results compared to selective SiO2-to-Si etching. A fluorocarbon film is present on the surfaces of all investigated substrate materials during steady state etching conditions. A general trend is that the substrate etch rate is inversely proportional to the thickness of this fluorocarbon film. Oxide substrates are covered with a thin fluorocarbon film (<1.5 nm) during steady-state etching and at sufficiently high self-bias voltages, the oxide etch rates are found to be roughly independent of the feedgas chemistry. The fluorocarbon film thicknesses on silicon, on the other hand, are strongly dependent on the feedgas chemistry and range from ∼2 to ∼7 nm in the investigated process...

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Study of the SiO2-to-Si3N4 etch selectivity mechanism in inductively coupled fluorocarbon plasmas and a comparison with the SiO2-to-Si mechanism

It has been found that in the etching of SiO2 using CHF3 in an inductively coupled plasma reactor of the planarized coil design, a thin steady state fluorocarbon film can play an important role in determining the rate of etching. This etching is encountered as the amount of bias power used in the SiO2 etching process is increased, and a transition from fluorocarbon film growth on the SiO2 to an oxide etching rate which is consistent with reactive sputtering theory is made. The observed presence of an intermediate region where etching occurs, although a steady state fluorocarbon film suppresses the etch rate from that expected for a reactive sputtering process, has been referred to as the fluorocarbon suppression regime. This work demonstrates the role of the steady state fluorocarbon film present on silicon dioxide during etching within the fluorocarbon suppression regime. X-ray photoelectron spectroscopy studies of the surfaces of partially etched SiO2 have shown a thinning of this film with increasing r...

Role of steady state fluorocarbon films in the etching of silicon dioxide using CHF3 in an inductively coupled plasma reactor

For various fluorocarbon processing chemistries in an inductively coupled plasma reactor, we have observed relatively thick (2–7 nm) fluorocarbon layers that exist on the surface during steady state etching of silicon. In steady state, the etch rate and the surface modifications of silicon do not change as a function of time. The surface modifications were characterized by in situ ellipsometry and x-ray photoelectron spectroscopy. The contribution of direct ion impact on the silicon substrate to the etching mechanism is reduced with increasing fluorocarbon layer thickness. Therefore, we consider that the silicon etch rate is controlled by a neutral etchant flux through the layer. Our experimental data show, however, that ions play an import role in the transport of silicon etching precursors through the layer. A model is developed that describes the etch kinetics through a fluorocarbon layer based on a fluorine diffusion transport mechanism. The model is consistent with the data when one or two of the fol...

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High density fluorocarbon etching of silicon in an inductively coupled plasma: Mechanism of etching through a thick steady state fluorocarbon layer

The influence of reactor wall conditions on the characteristics of high density fluorocarbon plasma etch processes has been studied. Results obtained during the etching of oxide, nitride, and silicon in an inductively coupled plasma source fed with various feedgases, such as CHF3, C3F6, and C3F6/H2, indicate that the reactor wall temperature is an important parameter in the etch process. Adequate temperature control can increase oxide etch selectivity over nitride and silicon. The loss of fluorocarbon species from the plasma to the walls is reduced as the wall temperature increased. The fluorocarbon deposition on a cooled substrate surface increases concomitantly, resulting in a more efficient suppression of silicon and nitride etch rates, whereas oxide etch rates remain nearly constant.

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Influence of reactor wall conditions on etch processes in inductively coupled fluorocarbon plasmas

Selective etching of SiO2 over polycrystalline silicon has been studied using CHF3 in an inductively coupled plasma reactor (ICP). Inductive powers between 200 and 1400 W, as well as pressures of 6, 10, and 20 mTorr were used in this study of the etch rate and selectivity behaviors for silicon dioxide, silicon, and passively deposited fluorocarbon films. Using in situ ellipsometry, the etch rates for all three of these materials were obtained for a self-bias voltage of −85 V, as well as passive deposition rates of fluorocarbon films. X-ray photoelectron spectroscopy has been used to examine the composition of steady-state fluorocarbon films present on the surfaces of polycrystalline silicon, and silicon dioxide during etching at high and low inductive powers. The dependence of the silicon etching behavior is shown to be clearly linked to the fluorocarbon polymerization and etching behavior. Thus, the polymerization and etching behavior of the fluorocarbon is the overwhelming parameter that governs the etc...

M. Schaepkens

Papers

Study of the SiO2-to-Si3N4 etch selectivity mechanism in inductively coupled fluorocarbon plasmas and a comparison with the SiO2-to-Si mechanism

Role of steady state fluorocarbon films in the etching of silicon dioxide using CHF3 in an inductively coupled plasma reactor

High density fluorocarbon etching of silicon in an inductively coupled plasma: Mechanism of etching through a thick steady state fluorocarbon layer

Influence of reactor wall conditions on etch processes in inductively coupled fluorocarbon plasmas

Selective etching of SiO2 over polycrystalline silicon using CHF3 in an inductively coupled plasma reactor