Robustness and reliability are among the most important requirements of semiconductor manufacturing processes. Their importance grows with the need to continuously improve yield and contribute to reduced cost of ownership. This necessitates including manufacturability considerations in the fundamental design of methods and instruments for in situ control of plasma etch processes. Optical monitoring methods and equipment for broadband (UV-VIS-IR) reflectometry have been developed to meet these advanced needs. The hardware is optimized for sufficiently accurate in situ metrology capabilities in a harsh plasma processing environment with minimal maintenance requirements. Novel model-based approaches are used to determine the absolute wafer state in real time. This facilitates compensating for incoming material variation with minimal reliance on operator input and interpretation. No special test structures on the wafer are required while the process chamber is only minimally modified for diagnostic equipment access. The methods facilitate development of fault detection schemes that help prevent misprocessing of wafers. Thus, demanding process control requirements are met on a wafer-to-wafer basis. The applicability of the technique has been successfully demonstrated for critical silicon-based etch applications such as shallow trench isolation (STI), recess for DRAM and embedded DRAM (eDRAM), and polysilicon gate.
Tighter control requirements for plasma etch processes drive the search for more accurate and robust methods for monitoring processes in situ. Conventional optical methods such as optical emission spectroscopy and interferometry, while easy to use, have their limitations especially in their ability to compensate for incoming material variations. As an alternative, we have successfully developed a broadband (UV-VIS-NIR) reflectometry-based approach for in situ monitoring of etch processes such as shallow trench isolation (STI) and recess etch processes. This approach enables us to estimate in real time the vertical dimensions of features of interest on patterned wafers. The approach has proven to be robust in that it works for a given application without modification for a variety of pattern densities and incoming material variations. It has proven to be easy to use in that there is minimal user/operator input required. We present results for a couple of applications that we have studied.
The waveguiding properties of sculptured nematic thin films (SNTFs) are investigated. A theoretical framework to determine the modal wavenumbers and modeshapes for guided wave propagation through these anisotropic microcolumnar mediums is presented. Numerical results are provided to illustrate the characteristics of guided wave propagation through C-SNTFs. The differences between guided wave propagation in such mediums and the corresponding isotropic thin films are highlighted.
The spectral signatures of non-axially excited, absorbing TFHBM layers are determined. The dispersive properties of the medium are described using a single-resonance Lorentzian model. Special emphasis is placed on the effect of absorption in the Bragg wavelength-zones, wherein the circular Bragg phenomenon occurs. Optical phenomena such as the optical rotation, circular dichroism and ellipticity transformation absorbing TFHBM layers are investigated. The effect of absorption on the functionality of TFHBM-based devices, such as multi-notch filters, are noted.
KEYWORDS: Thin films, Anisotropy, Ions, Contrast transfer function, Sputter deposition, Chemical species, Scanning electron microscopy, Electron microscopes, Information operations, Molecular aggregates
Sculptured thin films (STFs) are columnar thin films in which the growth direction is altered instantaneously by variations in the vapor incidence angle. By fixing the orientation of the substrate-surface to a glancing angle (approximately 1-30° from the substrate plane) where atomic self-shadowing effects are enhanced, and then rotating around the plane normal, it is possible to engineer a wide range of STF nanostructural shapes which have been classified generally as thin film helicoidal bianisotropic mediums (TFHBMs). If the column size remains constant with increasing film thickness (i.e. matchstick morphology), then the TFHBMs will have constant density with evolution, and existing theories can describe their optical behavior. Furthermore, many practical applications will require constancy with evolution. In this paper we show that essentially constant column size (widths are typically 10 - 100 nm) is obtained for simple motions of the substrate for TFHBM growth, whereas more complex motions involving rapid and abrupt changes in the angular velocity result in column size increases with evolutionary development (widths up to 200 - 500 nm for film thicknesses of 2 - 4μm). As the column sizes approach optical wavelengths, the assumption that the STF is a rotationally non-homogeneous continuum is invalid and will lead to complicated optical behavior and modeling. A classification scheme is proposed to understand the underlying mechanisms for column expansion, and it is based upon the deposition parameters of column growth rate in the column direction, angular rotation rate, and the vapor incidence angle, and their combined effects on the anisotropy of the atomic self-shadowing process. Approaches to controlling and possibly eliminating this column expansion are discussed and include ion bombardment during growth and its effects on the shadowing processes.
The concept of nanoscopic-to-macroscopic homogenization of a sculptured thin film (STF) into a unidirectionally nonhomogeneous continuum is presented. The global constitutive properties of linear STFs are connected to the so-called local or reference constitutive properties by rotation dyadics. The local properties are obtained using the Bruggeman formalism for dielectric as well as bianisotropic STFs. Limitations of the presented approach are discussed, and some avenues for further theoretical research are suggested.
As sculptured thin films (STFs) have a nano-engineered morphology (comprising 3 - 5 nm clusters) STFs with desired electromagnetic properties in the optical, infrared, millimeter wave and even microwave regimes can be tailored. With the development of specialized fabrication techniques on the upswing, device-oriented studies on STFs are gaining impetus. We focus on five possible applications of STFs: (1) laser mirrors and notch filters, (2) rugate-like filters, (3) optical gas concentration sensors, (4) optical interconnects, and (5) ultra-low permittivity barriers.
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