Interferometry, laser

There are a number of reasons that it is important to characterize the dissolution or development rate of any given resist. The main reasons tend to be for process control purposes, given that image discrimination in resists is based on differences in dissolution rates between the image and non-image areas. The two main techniques that are used to characterize the dissolution properties of a resist are laser interferometry and quartz crystal microbalance. Each of these techniques is reviewed below. 

The first use of laser interferometry in monitoring the dissolution rate of a resist during development was by Konnerth and Dill. The basis of their idea is shown in Fig. 11.28. A laser beam is directed toward the film, which is immersed in the developer. The reflected beam from the surface of the film and that reflected from the interface between resist and substrate interfere constructively or 

Nonogaki, T. Ueno, and T. Ito, Microlithography Fundamentals in Semiconductor Devices Fabrication Technology, Chapter 5, Marcel Dekker, New York (1998). 

Ito and C.G. Willson, Chemical amplification in the design of dry developing resist materials, Polym. Eng. Sci. 23, 1012 1018 (1983). 

Konnerth and F.H. DiU, In situ measurement of dielectric thickness during etching or devel oping processes, IEEE Trans. Electron. Dev. ED-22, 453 (1975) K.L. Konnerth and F.H. Dill, IOTA, a new computer controlled thin film thickness measurement tool, Solid State Electron. 15, 371 (1972). 

The development process produces final three-dimensional resist images. This is a critical process as a sinusoidal latent image generated by exposure must be converted to a step function in order to produce resist images with vertical wall profiles. Thus, it is important to understand the dissolution behavior of resist films in a developer (especially aqueous base). 

The study of the dissolution behavior involves measurements of film thickness as a function of time. Although the simplest procedure requires manual measurements of the initial thickness and the thickness after development for a given period of time to generate average dissolution rates, automated in situ thickness measurement methods are much more preferred as kinetics information is much more valuable than simple average dissolution rate data. Two methodologies are available laser interferometry and quartz crystal microbalance (QCM). 

---

Gidon, S., G. Garcin, and H. Behar (1984), Doppler Laser Interferometry with Light Transmission by Two Optical Fibers. In High Speed Photography and Photonics, Proc. SPIE 4, 91 (edited by M. Andre and M. Hugenschmidt), pp. 894-898. 

A typical shock-compression wave-profile measurement consists of particle velocity as a function of time at some material point within or on the surface of the sample. These measurements are commonly made by means of laser interferometry as discussed in Chapter 3 of this book. A typical wave profile as a function of position in the sample is shown in Fig. 7.2. Each portion of the wave profile contains information about the microstructure in the form of the product of and v. The decaying elastic wave has been an important source of indirect information on micromechanics of shock-induced plastic deformation. Taylor [9] used measurements of the decaying elastic precursor to determine parameters for polycrystalline Armco iron. He showed that the rate of decay of the elastic precursor in Fig. 7.2 is given by (Appendix)... 

Barker, L.M., Laser Interferometry in Shock-Wave Research, Exp. Mech. 12, 209-215 (1972). 

Typical approaches for measuring diffusivities in immobilised cell systems include bead methods, diffusion chambers and holographic laser interferometry. These methods can be applied to various support materials, but they are time consuming, making it onerous to measure effective dififusivity (Deff) over a wide range of cell fractions. Owing to the mathematical models involved, the deconvolution of diffusivities can be very sensitive to errors in concentration measurements. There are mathematical correlations developed to predict DeS as... 

Other devices and methods can also be applied, such as laser interferometry, which measures the change in the height of fuel in the tank using lasers, or acoustics methods that measure the sound of fluid escaping or entering the tank. 

A novel approach to determine the solvent concentration profile in a photoresist undergoing dissolution via fluorescence quenching and laser interferometry is introduced. Fluorescence arising from phenanthrene dye labels in a l-/im-thick polymethylmethacrylate)... 

In our previous paper (H), we introduced a novel experimental method to study the mechanistic details of solvent permeation into thin polymer films. This method incorporates a fluorescence quenching technique (19-20) and laser interferometry ( ). The former, in effect, monitors the movement of vanguard solvent molecules the latter monitors the dissolution process. We took the time differences between these two techniques to estimate both the nascent and the steady-state transition layer thicknesses of PMMA film undergoing dissolution in 1 1 MEK-isoproanol solution. The steady-state thickness was in good agreement with the estimate of Krasicky et al. (IS.). ... 

Experiments are reported on the dissolution rate and permeation rate for thin (1 nm) PMMA films exposed to liquid MEK. The films contain ca. 1 % of covalently-bound Phe, a fluorescent dye. By monitoring the dissolution rate by laser interferometry and the fluorescence quenching of Phe by MEK, we can determine ... 

A more recent technique utilizes laser interferometry. Again we quote from Ref 7 With the interferometer, the movement of a reflecting surface can be monitored as a function of time. The surface can be a free surface or in transparent materials a reflecting plane within or... 

A more detailed description of laser interferometry as it applies to particle velocity studies is to be found in Refs 11 12. Results of these studies will be discussed in Section IV EMV Method... 

ForIsopmpylnitrate ua = 1.49km/sec (Ref 9) Kennedy et al (Ref 11) and Nunziato et al (Ref 12) used laser.interferometry to obtain the particle velocity histories in PBX 9404 shown in Fig 11 for long-duration input pulses and in Fig 12 for short-duration pulses. The PBX 9404 targets were too thin (8 is target thickness) to detonate,-but particle velocity increase denoting reaction in the targets is clearly indicated. These particle velocity histories are qualitatively similar to those obtained in Ref 16, shown in Fig 4... 

Droplet-Size Measurements in Reacting Flows by Laser Interferometry... 

Laser Interferometry Type Thermal Expansion Meter LIX-1, Ulvac/Sinku-Riko, Inc., North American Liaison Office Kennebunk, ME. 

Whether or not a chemical process step has been successful is difficult to measure, since there are few on-line measurable electrical properties. For example, film thickness and grain structure of polycrystalline silicon can be measured after a deposition step. However, their effect on device performance might not show up until subsequent doping or patterning steps fail. Similarly, it is possible to measure etch rates on-line by laser interferometry, but the etch profiles must be checked by electron microscopy. Unexpected mask undercutting or undiscovered etch residues can result in subsequent contact and device lifetime problems. 

The surface stress (specific surface energy) can be measured by -> bending beam technique or by electrochemical -> Kosters laser interferometry [vii]. (See also -> surface stress measurements.)... 

Figure 2 shows the principle of electrochemical Kosters laser interferometry for the determination of changes of surface energy by the resulting deformation of an elastic plate. The height AZc of the center of the plate with respect to a plane at a given radius yields Ag from the appropriate form of Hookes law... 

Laser-interferometry Exc Ltd. No Yes Good Yes Some High Easy High... 

M. G. Jenkins, Ceramic Crack Growth Resistance Determination Utilizing Laser Interferometry, PhD Dissertation, University of Washington, Seattle, WA, 1987. 

The dissolution rate of the sample films during development was measured by laser-interferometry(4). A 5 mW He-Ne laser was used as the monitering light source and a silicon photodiode connected to a chart recorder was used as the signal detector. 

Laser interferometry was used to study the dissolution rates of selected films (16, 12) 632.8 nm wave-... 

Laser interferometry employs the principle of optical interference to recover the sought acoustic information from the light reflected from, or scattered by, a surface under ultrasonic vibration. Its non-contact nature makes laser probing a preferred alternative to contact methods in studying surface waves, their diffraction and damping by intrinsically rough surfaces. 

The technique used to measure the surface tension of foils in this work couples two well Imown technologies the zero creep technique for foils, and the technique of laser interferometry. The theory behind each of these techniques will be discussed briefly in order to develop the expressions necessary to generate the desired surface tension data which will be used to calculate the surface free energy. 

---