This paper discusses issues relating to the reliability and methods for employing high-cycle life testing in capacitive RF
MEMS switches. In order to investigate dielectric charging, transient current spectroscopy is used to characterize and
model the ingress and egress of charges within the switch insulating layer providing an efficient, powerful tool to
investigate various insulating materials without constructing actual MEMS switches. Additionally, an in-situ monitoring
scheme has been developed to observe the dynamic evolution of switch characteristics during life testing. As an
alternative to high-cycle life testing, which may require days or weeks of testing, a method for performing accelerated
life tests is presented. Various methods for mitigating dielectric charging are presented including: reduced operating
voltage, reduced dielectric area, and improved control waveforms. Charging models, accelerated life test results, and
high-cycle life test results for state-of-the-art capacitive RF MEMS switches aid in the better understanding of MEMS
switch reliability providing direction for improving materials and mechanical designs to increase the operation lifetime
of MEMS capacitive switches.
The uniformity of critical dimensions is an important aspect of photomask fabrication, and the etch process can be improved by optimizing the geometry of the focus ring that surrounds the mask. Previous experimental results have shown that the focus ring can have a dramatic impact on the variability of critical dimensions on the photomask. Simulations were performed with the Hybrid Plasma Equipment Model (HPEM) software to examine the impact of different focus ring geometries on the plasma characteristics and improve the understanding of the experimental data.
Accurate determination of endpoint is important for creating a repeatable process that maximizes sidewall profile angle and resist selectivity while maintaining a low etch bias. An Applied Materials EyeD (TM) spectrometer on the Tetra(TM) II photomask etch system is used to examine several endpoint methods to maximize flexibility and productivity. These methods include: slope changes to a single line, slope changes via a ratio of product and etchant species and slope changes of a linear combination of all slope changes. Endpoint identification is typically performed with a single spectral line. In addition, a method using neural networks, or principal component analysis (PCA) has also been created in order to fully optimize and characterize exact endpoint definition. Comparison between these methods will be discussed.
As mask features advance to the 65 nm technology node, the ability to develop advanced phase shifting masks with reliable and repeatable processes is becoming increasingly important. Changes in process conditions (i.e. power, pressure, gases, etc.), play an important role in the reduction of RIE lag, micro-trenching, loading and the improvement of sidewall profiles. In this study, the effects of changing process conditions on the TetraTM II Photomask Etch System were investigated. Process development was conducted to screen for a quartz etch process regime with enhanced performance.
Asymmetrically loaded patterns have been used to develop and optimize the chrome etch process on the TetraO II, the next -generation tool offered by Etec Systems. These asymmetrically loaded patterns offer unique challenges to the dry etch process by concentrating much of the chrome load in one section of the mask (usually one quadrant) while leaving the rest of the mask uniformly loaded. Numerical analysis of both the final chrome and the point-by-point etch
contribution has been implemented to allow accurate interpretation of etch results.
Chamber surface condition in high-density plasma etch reactors can dramatically affect process performance. The well-known “first wafer effect” in wafer etch processes is often reduced by a “seasoning” process which runs an appropriate etch chemistry on a dummy wafer prior to the etch of a production wafer. The seasoning process has proven to be an effective method for minimizing wafer process shift, but it has not been examined for photomask production using typical dry etch chemistries. In this work, a series of PR/Cr/Quartz photomasks were etched in a Etec Systems, Inc. Tetra photomask etch system with the goal of quantifying the amount of change in etch rate and critical dimension (CD's) following an isopropanol “wet” cleaning of the chamber, as well as the amount of seasoning necessary to minimize the observed process shift using a standard Cl2/O2/He chemistry. The chamber seasoning and etch processes were observed via in-situ recording of optical emission from the plasma reactor with a CCD array and monochromator. Alumina coupons affixed to different areas of the chamber prior to mask seasoning/etching were subjected to X-Ray Photoelectron Spectroscopy as well as Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS) to determine the identity of the chemical species deposited in the chamber during the seasoning/etching process. Results from these etching processes clearly indicated the presence of a “first mask effect,” which can be reduced by a seasoning process appropriate for the particular chemistry involved. Alumina coupon surface analysis revealed a negligible amount of deposition accumulating during the experiments.
The Etec Systems TetraTM photomask etch system is currently used to etch attenuated phase shift photomasks. Currently, MoSiON is a common film used for phase shifting. Either chrome or re sist can be used as a mask for etching this film. Because the quartz substrate etches with the same chemistry commonly used to etch MoSiON, precise endpoint control is necessary to meet the phase targeting requirements to create this type of phase-shifting mask. This paper will address techniques used to obtain precise endpoint control ofthe MoSiON-quartz boundary. Endpoint control is required for the precise phase targeting of 1 800 ± 1 .5° needed for advanced subwavelength patterning technologies. In this paper, optical emission spectroscopy is used to characterize and monitor chrome etch processes on the Etec Systems TetraTM photomask etch chamber. Changes in process conditions have been captured by time-averaged optical emission traces. Using multi-wavelength optical emission spectroscopy data collected during MoSiON etching, a fingerprint ofthe plasma can be taken. The fingerprint is used to detect changes in emission lines during the etch and determine the best wavelength for endpoint detection. Secondly, this paper will examine numerical methods ofendpoint optimization, including averaging, smoothing and derivative techniques.
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