Fabrication and Characterization of AlN-based, CMOS compatible Piezo-MEMS Devices

This paper details the development of high-quality, c-axis oriented AlN thin films up to 2 {\mu}m thick, using sputtering on platinum-coated SOI substrates for use in piezoelectric MEMS. Our comprehensive studies illustrate how important growth parameters such as the base Pt electrode quality, deposition temperature, power, and pressure, can influence film quality. With careful adjustment of these parameters, we managed to manipulate residual stresses (from compressive -1.2 GPa to tensile 230 MPa), and attain a high level of orientation in the AlN thin films, evidenced by < 5deg FWHM X-Ray diffraction peak widths. We also report on film surface quality regarding roughness, as assessed by atomic force microscopy, and grain size, as determined through scanning electron microscopy. Having attained the desired film quality, we proceeded to a fabrication process to create piezoelectric micromachined ultrasound transducers (PMUTs) with the AlN on SOI material stack, using deep reactive ion etching (DRIE). Initial evaluations of the vibrational behavior of the created devices, as observed through Laser Doppler Vibrometry, hint at the potential of these optimized AlN thin films for MEMS transducer development

Researching the Aluminum Nitride Etching Process for Application in MEMS Resonators

We investigated the aluminum nitride etching process for MEMS resonators. The process is based on Cl2/BCl3/Ar gas chemistry in inductively coupled plasma system. The hard mask of SiO2 is used. The etching rate, selectivity, sidewall angle, bottom surface roughness and microtrench are studied as a function of the gas flow rate, bias power and chamber pressure. The relations among those parameters are reported and theoretical analyses are given. By optimizing the etching parameters, the bottom surface roughness of 1.98 nm and the sidewall angle of 83° were achieved. This etching process can meet the manufacturing requirements of aluminum nitride MEMS resonator

Researching the Aluminum Nitride Etching Process for Application in MEMS Resonators

We investigated the aluminum nitride etching process for MEMS resonators. The process is based on Cl2/BCl3/Ar gas chemistry in inductively coupled plasma system. The hard mask of SiO2 is used. The etching rate, selectivity, sidewall angle, bottom surface roughness and microtrench are studied as a function of the gas flow rate, bias power and chamber pressure. The relations among those parameters are reported and theoretical analyses are given. By optimizing the etching parameters, the bottom surface roughness of 1.98 nm and the sidewall angle of 83° were achieved. This etching process can meet the manufacturing requirements of aluminum nitride MEMS resonator

Using Infrared Spectroscopy and Ellipsometry to Study Fluorination and Ligand-Exchange Reactions During Etching of Oxides and Nitrides

Over the last 60 years, the etching of materials has become a necessity for advancements in integrated circuits. As critical dimensions decrease it has become important to control the thicknesses of various features to the nanometer scale. Atomic layer etching (ALE) is a technique that has gained significance over the last 15 years. Recently thermally based atomic layer etching systems have been developed for many materials relevant for semiconductor manufacturing.First, the fluorination reaction during the ALE of aluminum oxide with HF and BCl3 is studied. Spectroscopic ellipsometry showed that the etch rate of Al2O3 can be controlled by increasing the pressure of the HF exposure. X-ray photoelectron spectroscopy (XPS) was used to model the fluoride thickness during HF fluorination and found good agreement between the fluoride thickness and etch rate. Infrared spectroscopy was also used to monitor the conversation of aluminum oxide to aluminum fluoride. Etching of ALD grown AlN was done with sequential exposures of HF and BCl3. Infrared difference spectra argued for fluorination and ligand exchange reactions. Single-crystal AlN was etched by XeF2 and static exposures of BCl3 with an etch rate of 0.62 Å/cycle. XPS was used to monitor the Al 2p region as well as contaminants left from the etching process. Quadrupole mass spectrometry (QMS) was also used to study the volatile etch products. AlCl3 was seen with BClxFy compounds. The etching of Al2O3 was investigated with HF and BCl3. Linear etching of Al2O3 was observed using infrared spectroscopy. Initial exposures of BCl3 showed a conversion reaction from Al2O3 to B2O3 but further cycles showed fluorination and ligand-exchange reactions. QMS results showed the etch product AlCl3 when cycling HF and BCl3. Spontaneous etching of B2O3 and TiO2 are studied as well. Infrared spectroscopy was utilized to monitor the ALD growth of B2O3 with BCl3 and H2O. Spontaneous etching was seen with sequential HF exposures. IR spectra during B2O3 etching showed there was B-F on the surface. B2O3 was able to be spontaneously etched down to 40ºC. Theory predicted etching at all temperatures down to 110K. QMS studies observed BF3 as the main volatile etch product. TiO2 ALD was done with TiCl4 and H2O. Etching was seen at temperatures of 100ºC and greater. Surface Ti-F bonding was seen during the spontaneous etching. QMS showed TiF4 was the main product during etching