Morphology and chemical termination of HF-etched Si3N4 surfaces

Liu, Li Hong; DeBenedetti, William J. I.; Peixoto, Tatiana; Gokalp, Sumeyra; Shafiq, Natis; Veyan, Jean-François; Michalak, David J.; Hourani, Rami; Chabal, Yves J.

doi:10.1063/1.4905282

Cited by 10 publications

(13 citation statements)

References 35 publications

(17 reference statements)

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“…The H-terminated Si(111) surface however, did seem to contain ammonium salts (very low surface polarity), having N-H vibrations (3160 cm -1 and 3345 cm -1 ) at higher wavenumbers indicative of a less H-bonded, constrained surface vibration. It is believed the dioxane solvent actually stabilized salt adsorption on the silicon surfaces instead of removing it, similarly to what has been observed on Si 3 N 4 surfaces after HF etching [4]. The F 1s peak was observed at 687.…”

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confidence: 67%

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Ammonia modification of oxide-free Si(111) surfaces

et al. 2016

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Amination of surfaces is useful in a variety of fields, ranging from device manufacturing to biological applications. Previous studies of ammonia reaction on silicon surfaces have concentrated on vapor phase rather than wet chemical processes, and mostly on clean Si surfaces. In this work, the interaction of liquid and vapor-phase ammonia is examined on three types of oxide-free surfaces-passivated by hydrogen, fluorine (1/3 monolayer) or chlorine-combining infrared absorption spectroscopy, X-ray photoelectron spectroscopy and first-principles calculations. The resulting chemical composition highly depends on the starting surface; there is a stronger reaction on both F-and Cl-terminated than on the H-terminated Si surfaces, as evidenced by the formation of Si-NH 2. Side reactions can also occur, such as solvent reaction with surfaces, formation of ammonium salt by-products (in the case of 0.2 M ammonia in dioxane solution), and nitridation of silicon (in the case of neat and gas phase ammonia reactions for instance). Unexpectedly, there is formation of Si-H bonds on hydrogen-free Cl-terminated Si(111) surfaces in all cases, whether vapor phase of neat liquid ammonia is used. First principles modeling of this complex system suggests that step edge surface defects may play a key role in enabling the reaction under certain circumstances, despite the endothermic nature for Si-H bond formation.

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confidence: 67%

“…Surface amination has become more important for applications in microelectronics, [1][2][3][4] biotechnology, [5][6][7][8] and nanotechnology. [1,6,9,10] Ammonia has been widely used to achieve surface nitridation and amination, particularly on silicon surfaces.…”

Section: Introductionmentioning

confidence: 99%

Ammonia modification of oxide-free Si(111) surfaces

et al. 2016

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“…SiO2 has a very sharp absorption peak at ~9.22 µm, resulting in highly dispersive characteristics in the LWIR [38]. Si3N4 has multiple vibrational phonon peaks in between 8 ̶ 12 µm, which correspond to a comparatively moderate dispersion and broader absorption profile in the LWIR [39]. For this reason, we choose Si3N4 as the lossy dielectric.…”

Section: Metal-dielectric Subwavelength Grating Cellsmentioning

confidence: 99%

Enhanced absorption per unit mass for infrared arrays using subwavelength metal–dielectric structures

Das¹,

Talghader²

2020

J. Opt. Soc. Am. B

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The absorption-to-mass ratio of the infrared arrays is enhanced to ~1.33 ̶ 7.33 times larger than the previously reported structures by incorporating two design characteristics: first, the coupling of evanescent fields in the air gaps around pixels to create effectively larger pixel sizes, and, second, the use of guided mode resonance (GMR) within the subwavelength metaldielectric gratings. The bilayer Ti-Si3N4 gratings achieve broadband long-wave infrared (LWIR,  ~ 8 ̶ 12 m) absorption by the combined effects of free carrier absorption by the thin Ti films and vibrational phonon absorption by the thick Si3N4 films. In the presence of GMR, this broadband absorption can be enormously enhanced even with low fill factor subwavelength grating cells. Further, the spacing and design of the cells can be modified to form a pixel array structure that couples the light falling in the air gaps via evanescent field coupling. Calculations are performed using the finite difference time domain (FDTD) technique. Excellent broadband absorption is observed for the optimized arrays, yielding maximum absorption of 90% across the LWIR and an average absorption-per-unit-mass (absorption/mass) per pixel of 3.45×10 13 kg -1 .

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“…On the opposite side, there is no widely recognized process for selectively removing the native oxynitride without affecting Si x N 4. Whereas etching kinetics of the Si x N 4 material were largely studied using HF, − HF/NH 4 F, , or potassium hydroxide (KOH) solutions, , few fundamental studies of the etching mechanisms are available. ,− ,, …”

Section: Introductionmentioning

confidence: 99%

“…28 Whereas etching kinetics of the Si x N 4 material were largely studied using HF, 29−34 HF/NH 4 F, 35,36 or potassium hydroxide (KOH) solutions, 37,38 few fundamental studies of the etching mechanisms are available. 39,[28][29][30]32,34 In addition to the selective removal of the native oxynitride on silicon nitride, the knowledge of the resulting chemical functions at the Si x N 4 surface after the wet etching represents another important challenge. The surface chemistry is still controversial: after HF etching, -NH x , 40 -SiH, 39,41 -SiOH, 42 and -SiF 29,32 have been mentioned as resulting surface chemical species.…”

Section: Introductionmentioning

confidence: 99%

Etching and Chemical Control of the Silicon Nitride Surface

Brunet

Aureau

Chantraine

et al. 2017

ACS Appl. Mater. Interfaces

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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 NHF 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-NH 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 H plasma treatment.

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Morphology and chemical termination of HF-etched Si3N4 surfaces

Cited by 10 publications

References 35 publications

Ammonia modification of oxide-free Si(111) surfaces

Ammonia modification of oxide-free Si(111) surfaces

Enhanced absorption per unit mass for infrared arrays using subwavelength metal–dielectric structures

Etching and Chemical Control of the Silicon Nitride Surface

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