RU-2861736-C1 - METHOD FOR MANUFACTURING ELEMENTS OF MICROELECTROMECHANICAL SYSTEMS BASED ON LITHIUM NIOBATE AND LITHIUM TANTALATE

RU2861736C1RU 2861736 C1RU2861736 C1RU 2861736C1RU-2861736-C1

Abstract

FIELD: microelectronics; microsystem technology. SUBSTANCE: invention relates to methods for thinning elements for microelectromechanical systems (MEMS) based on lithium niobate (LiNbO 3 , LN) and lithium tantalate (LiTaO 3 , LT), and can be used to create sensitive and highly stable microelectromechanical sensors and resonators, including bimorph membranes, cantilever and tuning fork elements, as well as acousto-optoelectronic devices. The method for manufacturing elements of microelectromechanical systems based on lithium niobate and lithium tantalate includes carrying out a reducing annealing in a furnace of plates of oxide ferroelectric material in an oxygen-free atmosphere at a pressure of not more than 2 Pa and a temperature of 600-1100°C for 4 hours, then local laser thinning of the reduced crystal is carried out using a pulsed laser source in the near-infrared range of the spectrum with an average output radiation power of at least 10 W, with a pulse frequency of 10-50 kHz, with a linear speed of 100 mm/s, then the crystal is subjected to oxidative annealing at a temperature of 400°C for 1 hour. EFFECT: providing fast and manufacturable thinning of thick single-crystal plates of lithium niobate and lithium tantalate, compatible with planar MEMS technology, to obtain microelectromechanical elements of small thickness and low surface roughness while maintaining the original ferroelectric domain structure and single-crystal perfection of the material. 1 cl, 2 dwg

Inventors

KISLYUK ALEKSANDR MIKHAJLOVICH
Manzov Andrej Andreevich
Maksumova Evelina Eduardovna
KUBASOV ILYA VIKTOROVICH
Kuts Viktor Viktorovich
Turutin Andrej Vladimirovich
Temirov Aleksandr Anatolevich
MALINKOVICH MIKHAIL DAVYDOVICH
PARKHOMENKO YURIJ NIKOLAEVICH
Kiselev Dmitrij Aleksandrovich
IVANOV VLADIMIR PAVLOVICH

Dates

Publication Date: 20260508
Application Date: 20251218

Claims (1)

A method for manufacturing elements of microelectromechanical systems based on lithium niobate and tantalate, which includes carrying out recovery annealing in a furnace of plates of oxide ferroelectric material in an oxygen-free atmosphere at a pressure of no more than 2 Pa and a temperature of 600-1100°C for 4 hours, followed by local laser thinning of the reduced crystal using a pulsed laser source in the near infrared range of the spectrum with an average output radiation power of at least 10 W, with a pulse frequency of 10-50 kHz, with a linear speed of 100 mm/s, then the crystal is subjected to oxidative annealing at a temperature of 400°C for 1 hour.

Description

The invention relates to the field of microelectronics and microsystems technology, namely to methods for thinning elements for microelectromechanical systems (MEMS) based on lithium niobate (LiNbO 3 , LN) and lithium tantalate (LiTaO 3 , LT), and can be used to create sensitive and highly stable microelectromechanical sensors and resonators, including bimorph membranes, cantilever and tuning fork-shaped elements, as well as acousto- and optoelectronic devices. LN and LT belong to a class of uniaxial ferroelectric oxide crystals with pronounced piezoelectric, pyroelectric, and electro-optical properties. These materials are characterized by optical transparency, high Curie temperatures, and chemical resistance, making them widely used in acoustoelectronic, optoelectronic, and nonlinear optical devices. MEMS based on LN and LT have been actively developed in the last decade. The importance of these materials for MEMS is confirmed by a number of studies on actuators, magnetoelectrics, acoustic resonators, and filters. MEMS elements based on LN and LT are typically implemented as thin (usually no more than 100 µm thick) suspended membranes, beams, cantilevered, and tuning-fork-shaped resonators. Their fabrication methods can be broadly divided into two groups: methods for forming thin films of micron and submicron thickness directly on a substrate, and methods for processing or thinning single-crystal wafers of initially greater thickness. Methods for forming thin-film MEMS elements based on LN [Lee T. H. et al. Investigation of LiNbO3 thin films grown on Si substrate using magnetron sputter //Materials Science and Engineering: B. - 2007. - Vol. 136. - No. 1. - Pp. 92-95.] and LT [Nougaret L., Combette P., Pascal-Delannoy F. Growth of lithium tantalate thin films by radio-frequency magnetron sputtering with lithium-enriched target //Thin Solid Films. - 2009. - Vol. 517. - No. 5. - Pp. 1784-1789.] by epitaxial growth methods are known. This method makes it possible to obtain thin LN and LT films with a thickness from tens of nanometers to several micrometers, which is convenient for integrating the elements into a planar production process. A disadvantage of known methods is the difficulty of simultaneously ensuring correct crystallographic orientation and stoichiometry during growth. The resulting films have a poly- or nanocrystalline structure with a high defect density, increased leakage currents, and significantly worse ferroelectric and piezoelectric properties compared to single crystals, limiting the quality factor and stability of MEMS resonators. Deposition on inappropriate substrates leads to high residual stresses, increased roughness, and the formation of microcracks and even film delamination during heat treatment or thermal cycling, which is especially critical for suspended membranes and beams in MEMS structures. The second group includes methods for producing single-crystal MEMS elements based on LN [Shao G. et al. Ferroelectric domain inversion and its stability in lithium niobate thin film on insulator with different thicknesses // AIP Advances. - 2016. - Vol. 6. - No. 7.] and LT [Yan Y. et al. Wafer-scale fabrication of 42° rotated Y-cut LiTaO3-on-insulator (LTOI) substrate for a SAW resonator // ACS Applied Electronic Materials. - 2019. - Vol. 1. - No. 8. - Pp. 1660-1666.] on an insulating substrate, which use ion slicing of crystals and their subsequent connection to the substrate with a metal electrode layer. The thickness of such thin single crystals is submicron. A disadvantage of these methods is that such crystals have an unstable ferroelectric structure, which is necessary for the long-term operation of MEMS sensors. Furthermore, the crystals themselves, produced by ion slicing, contain a significant number of defects and internal stresses, making the thin layers mechanically brittle. The presence of interlayer boundaries and the difference in thermal expansion coefficients between the crystal and the substrate further increases the risk of cracking and delamination during heat treatment and thermal cycling. A method for cutting and thinning LN and LT wafers using ion-beam etching is also known [US5242537A, published September 7, 1993]. This method allows for thinning wafers to micron thicknesses with very low roughness without degrading the ferroelectric properties. However, the method has an extremely low material processing speed and cannot be applied to planar MEMS technology. Methods for profiling and thinning LN [US4750979A, published June 14, 1988] and LT [CN111627811 A, published June 10, 2020] wafers using reactive ion etching are known. This method is highly compatible with planar technology and enables the formation of MEMS structures in a single lithographic cycle. However, ion etching is characterized by a relatively low material removal rate and pronounced edge effects, including under-etching of the pattern under the mask and profile distortion, making this method ineff