Andrea Conte

Stable and Reliable Q-Factor in Resonant MEMS with Getter Film

The objective of this work was to show that the Q-factor of MEMS resonators can be increased and stabilized with the use of getters

A new model for vacuum quality and lifetime prediction in hermetic vacuum bonded MEMS

In many MEMS applications the level of vacuum is a key issue as it directly affects the quality of the device, in terms of response reliability. Due to the unavoidable desorption phenomena of gaseous species from the internal surfaces, the vacuum inside a MEMS, after bonding encapsulation, tends to be degraded, unless a proper getter solution is applied. The in situ getter film (PaGeWafer®) is recognised to be the most reliable way to get rid of degassed species, assuring uniform, high quality performances of the device throughout the lifetime. Moreover, post process vacuum quality control and reliability for hermetic bonding is extremely important for overall device reliability and process yield. In this paper we will discuss the main factors that are critical in the attainment of vacuum and will present a novel calculation model that enables the prediction of vacuum level after bonding, making also possible the estimate of the lifetime. Furthermore, a new analytical method based on the residual gas analyses (RGA) will be presented that gives the main characteristics of the materials. Modeling and simulation work support the process optimization and system design.

The Transmission Factor Method: in‐situ Characterization of Getter Coated Pipes

Particle accelerators and synchrotron light source need low residual pressure during operating conditions. In specific applications like narrow‐gap insertion devices, NEG coating has proved to be very effective. ASTM F798‐82 standard is the common characterization method for the sorption performance of getters. In the case of getter coated pipes, the measurement is conducted “offline” on a sample (coupon), suitably positioned inside the chamber to be coated and removed after the process. Although this approach is suitable to guarantee the control of the process, in‐situ characterization should be useful to evaluate residual pressure during the operating conditions. A different measurement technique (Transmission Factor Method) is here described. It is based on the measurement of pressures ratio at the inlet and the outlet of a coated pipe, under a flow of test gas. A calibration curve is calculated using a modellistic approach and permits to evaluate sticking probability of the coated surface from the pressure ratio. Preliminary experimental results about the characterization of this getter will be shown. Keywords: Getter sorption measurement.

Development of thin film getters for assuring high reliability and long lifetime to crystal oscillators

The shrinkage of hermetic packages for crystal oscillators poses tremendous challenges to keep constant the pressure during the lifetime of the device because of the considerable effect of surface outgassing and gas permeation. Getters have been used over tens of years in the vacuum tube industry to keep constant vacuum inside sealed devices. To provide a suitable getter solution to miniaturized hermetic packages, a few micron thick getter film has been developed and placed on the lid of the hermetic packages. This technical solution, the getter thin film on the lid, assures a long lifetime and stability to hermetically packaged oscillating structures.

Outgassing and Gettering

Outgassing is an unavoidable issue and although the cleaning process and long baking are carried out, the effect can be limited only by using the getter technology. This technology absorbs the residual gases trapped in the device during the process and maintains the pressure at a very low level for the required lifetime, limiting the gas flux. It has been described that there are gases remaining inside MEMS devices that need a vacuum or other stable pressure to operate properly. The MEMS packaging technology moved from hermetic vacuum discrete packages to vacuum wafer-level packages. Conventional packaging of microelectronic and optoelectronic devices is usually stable and not affected by the external environment except for a few specific cases. Vacuum wafer-level packaging is a very effective technique to produce low-cost, hermetically sealed packages for micromachined sensors and actuators. The main contamination source is the leakage and outgassing phenomena. The leakage is mainly caused by defects in the bonding frame and can be solved by a suitable improvement of the technology or accepting a limited yield in the MEMS production. In the case of outgassing a technically viable solution to assure a long lifetime and high reliability to MEMS device is the integration of a getter film. This has also been explained in detail.

Lifetime prediction in vacuum packaged MEMS provided with integrated getter film

Thin-film getter integration is one of the key technologies enabling the development of a wide class of MEMS devices, such as IR microbolometers and inertial sensors, where stringent vacuum requirements must be satisfied to achieve the desired performances and preserve them for the entire lifetime. Despite its importance, the question about lifetime prediction is still very difficult to answer in a reliable way. Here we present an experimental approach to the evaluation of lifetime, based on an accelerated life test performed varying both the storage conditions and the getter area. A test vehicle based on a resonator device was used. The hermeticity was evaluated by means of specific leak testing, while MEMS behavior during the ageing test was studied monitoring device functional parameters and by residual gas analysis (RGA). Unexpected results were observed leading to the discovery that methane is pumped by the getter below 100°C. These results served as the inputs of a suitable model allowing extrapolating the device lifetime in operating? conditions, and pointed out that RGA is an essential tool to correctly interpret the aging tests.

Chapter Forty – Outgassing and Gettering

Publisher Summary Outgassing is an unavoidable issue and although the cleaning process and long baking are carried out, the effect can be limited only by using the getter technology. This technology absorbs the residual gases trapped into the device during the process and maintains the pressure at very low level for the required lifetime, limiting the gas flux. It has been clearly described that there are gasses remaining inside MEMS devices that need a vacuum or other stable pressure to operate properly. The MEMS packaging technology moved from hermetic vacuum discrete packages to vacuum wafer-level pack- ages. Conventional packaging of microelectronic and optoelectronic devices is usually stable and not affected by the external environment except for a few specific cases. Hydrogen Vacuum wafer-level packaging is a very effective technique to produce low-cost, hermetically sealed packages for micromachined sensors and actuators. The MEMS devices requiring a vacuum to operate properly are shown in pressure level is a key parameter for the quality of the MEMS devices. The main contamination source is the leakage in the bonding and outgassing phenomena. The leakage is mainly caused by defects in the bonding and can be solved by a suitable improvement of the technology or accepting a limited yield in the MEMS production. A technically viable solution to assure a long lifetime and high reliability to MEMS device is the possibility to integrate a getter film. This has also been explained in detail.

NEG (Non Evaporable Getter) pumps for organic compounds and water removal in EUVL tools

One of present EUVL challenges is to reduce as much as possible the organic compounds and water partial pressures during the lithographic process. These gases can in fact interact with sensitive surfaces and, in the presence of EUV radiation, decompose to generate carbon-based films and oxides, which are detrimental to the optics, reducing its performance, lifetime and significantly increasing the equipment total cost of ownership. With this respect, use of Non Evaporable Getter (NEG) pumps seems particularly attractive. Getter pumps are very clean, vibration-free, compact, able to deliver large pumping speed for all active gases, including water and hydrogen. In the present paper, we report for the first time the results of specific tests aimed at measuring the pumping speed for some selected organic compounds, namely toluene and decane (n-decane). The study shows that getter pumps can effectively sorb these large organic molecules with high speed and capacity. Speed and capacity increases when operating the getter cartridge at moderate temperature (e.g. 150-200°C), however remarkable sorption is achieved, even at room temperature, without any power applied. When coupled with turbo-molecular pumps NEG pumps have therefore the potential to improve the ultimate vacuum and mitigate the carbon/oxygen contamination in a UHV lithographic system.

Nonequilibrium processes on TiV surface induced by activation and absorption of gases

X-ray photoelectron spectroscopy (XPS), high-resolution scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to investigate the effects of thermal activation in the surface chemistry and morphology of a Ti70V30 gettering alloy. The samples were analysed as-received (after in-air exposure) and after different annealing treatments up to 600°C. For temperatures greater than 270°C a progressive reduction of the TiO2, initially found on the as-received samples, to TiOx (x<2) occurs. The high concentration of vacancies in the TiOx (x<2) lattice ensures that the surface oxide layer is transparent towards gas diffusion at relatively low temperatures. The activation process is accompanied by a roughening of the surface, probably induced by the condensation of vacancies in the non-stoichiometric TiOx lattice. Vanadium appears to exert some promoting effect on this mechanism. In the 300–500°C temperature range a fraction of the carbon-based contamination on the surface forms carbides. These carbides start to decompose at temperatures above 550°C.

Non Evaporable Getter (NEG) Coatings for Vacuum Systems in Synchrotron Radiation Facilities

Non evaporable Getter (NEG) films, sputter deposited onto the internal surfaces of vacuum chambers, have been proposed by CERN to substantially reduce the gas pressure in UHV‐XHV systems. The NEG film acts as a conductance‐free distributed pump inside a chamber. Being a barrier for gases it also reduces thermal out‐gassing, thus allowing the achievement of very demanding pressure conditions. These features are ideal for very narrow, conductance limited chambers, like Insertion Devices, which cannot be always efficiently pumped by ordinary means. Recent investigations have also shown that NEG coatings do present additional interesting features, like low secondary electron yield and low gas de‐sorption rates under ions, electrons and photons bombardment, compared to traditional technical surfaces. Experimental tests, carried out in several high energy machines and synchrotron radiations facilities have so far confirmed the benefits of NEG films in term of better vacuum, longer beam life time and stability, ...