MODEL 2010/M PRISM COUPLER APPLICATION OVERVIEW
For a broad range of applications, the Model 2010/M offers unique advantages compared to traditional film measurement methods:
Optical waveguides: The Model 2010/M is ideally suited to characterization of materials and processes used in optical waveguide fabrication. The system provides routine display of the mode pattern (reflected intensity vs angle of incidence), effective mode indices, and calculation of thickness and index for step index guides and index gradients for graded index guides. In addition, a loss measurement option, based on the moving fiber approach, is available. This apparatus has been tested on guides with loss down to the 0.1-0.2 db/cm range with good results. A high resolution rotary table (a no-charge option) provides effective index resolution of ±.00005. As many as three lasers in addition to the standard 633 nm HeNe can be built into the system for multiple wavelength operation (popular secondary wavelengths include 830, 980, 1310, and 1550 nm) and germanium detectors are available for wavelengths beyond 1100 nm. Alternatively, an external port is available to allow use of the system with user-supplied lasers in the wavelength range 400-1600 nm. Multiple wavelength systems (with secondary lasers either built-in or supplied by the user) incorporate multiple beamlines and beamsplitters to permit rapid (30-second) changeover between wavelengths. A variety of coupling geometries can be accommodated, and stock prisms are available to span the effective index range of 1.30?3.35. For further information, please request Application Note 105 -- "Optical Waveguide Characterization."
Index measurement of bulk/substrate materials/liquids: The 2010/M provides rapid (5 second) measurements of the refractive index of glasses, polymers, plastics, garnets and other materials (both rigid and flexible) with a routine resolution of ±0003 (±.00005 with a high resolution rotary table). Bulk materials must be reasonably flat (fine polish or optical flatness not required) or slightly convex. Index measurement range extends from 1.0-3.35 and no matching fluids are required. Liquids are also measurable. For complete information, please request Application Note 106 - "Bulk Material/Thick Film Measurement".
Free-standing polymers: In-plane and perpendicular plane index for free-standing polymer films, including flexible films, are easily measured by the Model 2010/M without the use of toxic or corrosive index matching fluids. In-plane refractive index can also be measured along any arbitrary in-plane direction by a simple rotation of the sample about the coupling point. Measurement of x, y and z indices permits measurement of density, crystallinity and orientation. Indices ranging from 1 to 2.6 are easily measured. Measurements are rapid (typically 20 seconds) and free of operator subjectivity. In some cases, information concerning index gradients in the material vs depth is obtainable, particularly in the case of high index surface skins. For further information, please request Application Note 107 - "Measuring Index Anisotropy of Free-Standing Polymer Films".
Surface plasmons: For biological and sensing applications, the 2010/M can used to measure surface plasmon resonances and shifts in resonances.
dn/dT measurements: Index vs temperature can be measured from room temperature up to 150-200E C.
Materials for display technologies: Since the prism coupling technique is easily applied to clear substrates, the 2010/M is well suited to measurements (including birefringence) of films used in the manufacture of LCD's and other display technologies.
Polymers/polyimides/photoresists: Because, in typical applications, these films are relatively thick and often optically absorbing, prism coupling is unmatched for ease and accuracy. Virtually every stage in the processing of these films (hard or soft bake, optical exposure or polymerization, and development) results in changes to thickness, index and dispersion (index vs wavelength). With its ability to resolve slight index changes, the 2010/M is the ideal tool to monitor film parameters throughout the complex processing of these films. As examples, degree of solvent removal following bake, and thus bake consistency, can be monitored via refractive index measurements, as can refractive index or thickness changes following exposure. In addition, these films often exhibit significant index/dielectric constant anisotropy, easily measured with the TM option. For further information, please request Application Note 102 - "High Accuracy Measurements of Resists, Polyimides, and Polymers."
Plasma nitride or oxynitride: These films have highly variable refractive index and dispersion (refractive index variation with wavelength) which makes accurate thickness measurement difficult with techniques which rely on spectrophotometry (optical interference vs. wavelength). Moreover, in typical applications, these films are usually thick and often absorbing, factors which can lead to inaccuracies with ellipsometer measurements. The 2010/M provides direct, high accuracy thickness results, fully corrected for index, dispersion, and absorption, and NIST standards for index and NIST-traceable standards for thickness are available. In addition, the high accuracy index result, a sensitive indicator of overall run-to-run film consistency, makes it easy to track variations in the performance of film deposition equipment. Dual-layer films of nitride over oxynitride or oxide and oxynitride over oxide are also measurable (see "Multilayer Films" section below).
Low-k or other interlevel dielectrics: Low-k polymer or dielectric films have highly variable optical properties which make them difficult to measure by spectrophotometer-based techniques. In addition, since interlevel dielectrics are relatively thick, ellipsometer measurements are often difficult. Not only does the 2010/M measure such films with ease, but its ability to measure both in-plane and perpendicular plane index allows determination of dielectric constant anisotropy.
Doped oxides: The 2010/M's unrivaled refractive index resolution provides a sensitive and quick (20 second) measurement of phosphorus content in doped silicon dioxide immediately after deposition. It is by far the quickest, simplest, and most economical way of monitoring phosphorus concentration on a routine basis, and provides a resolution and accuracy comparable to other popular techniques. For further information, please request Application Note 101 - "Rapid Measurement of Phosphorus Concentration in Doped Oxides."
Multilayer Films: For dual film structures in which the upper film has the higher index (e.g., nitride over oxide, or resist/polyimide over oxide), the 2010/M offers straightforward thickness and index measurements of one or both films. As an example, dual layer dielectrics such as nitride or oxynitride over oxide or oxynitride over oxide (both films deposited in a single deposition run), can easily be measured. For this application, the 2010/M measures thickness and index for both films, provided only that the user supplies a rough starting value for the lower film index. For the case of structures with more than two film layers, if the top film index exceeds the index of the layer immediately below, the top film is measurable. If the second film index exceeds the index of the film immediately beneath, it also is measurable. Finally, thick upper films over relatively thin lower films of higher index are often measurable with some slight loss in thickness accuracy (index accuracy is only minimally affected). For further information, please request Application Note 103 -- "Multilayer Film Measurements."
Films on metals and other semiconductors: The Model 2010/M provides high accuracy measurements of films on high index semiconductor substrates such as GaAs or germanium. Moreover, measurements of films on metallic or metal coated substrates are straightforward and are insensitive to the surface properties of the metal (i.e., smoothness/reflectivity). Thickness limits and performance are virtually indistinguishable from measurements on silicon.
Magnetic thin film head materials: The 2010/M provides straightforward thickness and index measurements of thin and thick alumina and other films used in magnetic thin film head manufacture. In addition, the VAMFO option permits high accuracy, non-contact measurements of thickness only for films thicker than approximately two microns. Measurements can be made on both bare and metal coated substrates.
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