The echelle grating, with a high spectral resolution and large angular dispersion, is the core component of high-resolution spectrometers. The main preparation method of echelle grating is mechanical holographic lithography combined with ion beam etching and wet etching. The gratings fabricated by the traditional mechanical method have a high cost, a rough groove surface, and a Roland ghost. The holographic lithography combined with ion beam etching can hardly fabricate echelle gratings and has a long production cycle. The wet etching method is a good supplement to the preparation method, and ultraviolet (UV) lithography combined with wet etching has the advantages of few equipment requirements, a low preparation cost, a short preparation period, little stray light, an accurate blazed angle, etc. At present, domestic research on echelle gratings is mostly on the design and application of instruments with echelle gratings. The research on the manufacturing technology of echelle gratings, especially wet etching technology, starts late and has few reports. The diffraction efficiency and groove quality of most silicon-based echelle gratings reported in the existing papers are low, and thus, they cannot be applied in practice. To meet the spectral requirement of the high-resolution spectrometer in near-infrared (NIR) bands (800-1100 nm), this paper chooses the wet-etched silicon echelle grating with an apex angle of 70.52° instead of the traditional echelle grating with an apex angle of 90°. In addition, the factors affecting the quality of the wet-etched grating are analyzed. It is necessary to develop an echelle grating that can meet the requirement of instruments and has high groove quality and practical application capability.

According to the crystal characteristics of (100) silicon and grating working conditions given by optical design, the electromagnetic field distribution is solved by the finite-element numerical calculation method, and the diffraction efficiency of working orders is obtained. On this basis, the diffraction characteristics of the silicon echelle grating in the working bands can be analyzed theoretically to obtain the grating factors affecting the diffraction efficiency. In the experiment, the photoresist mask is prepared by UV lithography, and the mask patterns are transferred to the SiO₂ layer by inductively coupled plasma etching. Finally, the grating grooves are made by wet etching. After the fabrication of gratings, the diffraction efficiency of gratings is measured by the tunable laser and detector. The roughness of groove surfaces is measured by the three-dimensional (3D) optical surface profiler. The spacing of the grating grooves and the blazed angles are measured by the scanning electron microscope.

The mask collapse problem in wet etching is explained through experiments. It is proposed that during wet etching, samples can be periodically taken out for observation with an optical microscope to prevent the collapse of the mask caused by over-etching. In addition, the etching process can be controlled better by this method to maintain the consistency and repeatability of gratings. The method of pre-etching is applied to the fabrication of silicon echelle gratings, which can improve the precision of crystal alignment to 0.015° and is used to solve the problem of overly large sidewall roughness of silicon gratings. In this paper, the sidewall roughness of the gratings is less than 1 nm, measured by a 3D optical surface profiler in the range of 120 μm×3.5 μm. It lays the foundation for the fabrication of high-quality silicon gratings. Compared with other fabrication methods of echelle gratings, UV lithography combined with wet etching greatly reduces the production cost. Moreover, the fabricated echelle gratings have a smoother groove surface and a more accurate blazed angle.

In this paper, the diffraction characteristics of the silicon echelle grating with a groove density of 42 lp/mm and an apex angle of 70.52° are simulated and analyzed in NIR bands (800-1100 nm). It is known that the width of the platform is one of the main factors affecting the diffraction efficiency, and the diffraction efficiency curves of working orders in the free spectral range have good consistency. A symmetrical V-shaped groove grating with a groove density of 42 lp/mm, a blazed angle of 54.74°, and an effective area greater than 46 mm×28 mm is fabricated on a silicon substrate by UV lithography and the wet etching technique. The key factors affecting the quality of the silicon grating in the fabrication process are analyzed and discussed. The experimental measurement shows that the diffraction efficiency of the grating is 45%-55% at the corresponding blazed wavelength of working orders, which meets the requirement of the index. The main reasons why the measured diffraction efficiency is lower than the design value are discussed, and the value calculated by scanning electron microscope data is analyzed. The successful development of silicon echelle gratings in this paper can verify the feasibility of wet-etched gratings in the formal application.