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 Tetra<sup>TM</sup> II Photomask Etch System were investigated. Process development was conducted to screen for a quartz etch process regime with enhanced performance.
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.
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.
Uniform radical distribution in the etching plasma is essential to meet chrome critical dimension (CD) uniformity for future technology nodes on chrome masks. The Etec Systems Tetra photomask etch chamber utilizes an alumina focus ring in order to optimize the etch uniformity of the chrome mask by minimizing gas flow effects and shaping the radial distribution of the etching radicals over the mask surface. This paper describes a systematic investigation to optimize the current focus ring, in order to improve etch critical dimension uniformity. The focus ring (FR) optimization work was made possible by manufacturing a modular focus ring that allowed the geometry to be varied at different heights and diameters. The circular shape of the modular focus ring, along with the height and diameter combinations, has a large influence on the etch performance at the mask corners and edges. The underlying mechanism was investigated by modeling and simulation. Based on simulation results the focus ring geometry was varied and the optimum FR configuration was found. The critical dimension uniformity could be adjusted on uniformly patterned masks with different pattern loads to meet production specifications.
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.
Demands on critical dimension specifications increase with the continuous shrinking of design rules. In order to meet sub-0.13μm specifications with precise process control, a better understanding of the etching chemistry and surface reactions need to be achieved. Optical emission spectroscopy (OES) is frequently used in the photomask community as a diagnostic for calling endpoint, but is often underutilized in process development. In-situ measurements, like OES, need to be utilized and correlated to post-etch metrology measurements in order to provide a larger picture of the etch process.
In this paper, OES is used to characterize and monitor chrome etch processes on the Etec Systems Tetra photomask etch chamber. Changes in process conditions, such as source power, He percentage, pressure, and Cl<sub>2</sub>:O<sub>2</sub> flow ratios have been captured by time-averaged optical emission traces. The OES data of the plasma, along with SEM pictures of line profiles, are used to gain insight in process optimization for the etching of chrome.
In this paper, optical emission spectroscopy is used to characterize and monitor chrome etch processes on the Etec Tetra photomask etch chamber. Changes in process conditions, such as source power, bias power, pressure, and gas flows have been captured by time-averaged optical emission traces. Using multi-wavelength OES data collected during chrome etching, a fingerprint of the plasma was taken. The fingerprint was generated using a principal component analysis (PCA) technique, which detects spectral correlation between multiple wavelengths. The PCA reduces the dimensionality of the multi-wavelength OES and extracts just the most relevant information. The new variables are created as linear combinations of the original variables. The new principal component peaks diminish more than the original peaks, allowing strong endpoint detection for a 1 percent chrome-loaded mask.