Richard N. Savage

Development and characterization of a 9-mm inductively-coupled argon plasma source for atomic emission spectrometry

Abstract A new 9-mm (i.d.) inductively-coupled plasma (ICP) torch is described which supports a stable, analytically useful plasma at less than 500 W of r.f. power and 7 l min -1 total argon gas flow. Detection limits, working curves and other analytical characteristics of the new device are compared with those of both a miniature (13-mm i.d.) and conventional (19-mm i.d.) ICP. Although temperatures of the new plasma are somewhat lower than those in the larger plasmas, the new system offers promise for future, miniaturized ICP instruments.

Characteristics of the Background Emission Spectrum From a Miniature Inductively-Coupled Plasma

Abstract The spectral characteristics of the background radiation emitted by a miniature inductively-coupled plasma (i.c.p.) are carefully examined and methods for reducing undesirable features discussed. The complex nature of the background emission spectrum for the mini-i.c.p. indicates that careful line selection criteria and background correction procedures should be employed. Extending the torch coolant tube to the bottom of the region being observed in the plasma proved to be the most effective method for reducing undesirable spectral band features. Acute changes in background emission levels with r.f. power and nebulizer gas flow rates emphasize the need for careful control of these parameters to achieve high precision. Comparison between mini-i.c.p. and conventional i.c.p. spectra reveals the basic similarity of the two sources.

In-situ film thickness measurements for real-time monitoring and control of advanced photoresist track coating systems

This paper will explore the methodologies of real-time measurement of photoresist film thickness on silicon wafers using multi-wavelength reflection interferometry. Reflected light from the wafer’s surface, containing the interference profile, is collected in-situ via a fiber optic cable and film thickness is determined in real-time via a pattern recognition algorithm. The instrumentation used to make this measurement and its application towards optimizing track performance during spin-coating and bake will be discussed. Data demonstrating basic thickness versus spin-time and thickness versus bake-time profiles acquired on-line without process disruption will be presented along with its utilization towards minimizing process set-up and machine qualification. Moreover, the advantages of characterizing film thickness on-line and in real-time will be reviewed.

Enhancement of Pneumatic Nebulization Efficiency through Application of an Electric Field.

A technique is described for reducing the size of aerosol droplets produced by a pneumatic nebulizer of the kind commonly used in flame or plasma spectrometry. The technique involves the application of an electric field to the tip of the nebulizer, resulting in an induced surface charge on the liquid being nebulized. In turn, the surface charge reduces the liquids surface tension and results in the generation of a finer aerosol. In this study, the effect of the electric field is quantified in terms of the spatial dispersion and size distribution of aerosol droplets formed in the presence and absence of the field. Droplet size distributions, obtained using the MgO impression technique and analyzed using log-normal and upper-limit functions, reveal a 63% decrease in the volume mean droplet diameter in the fields presence. As a result, this system is expected to be useful in both flame and plasma spectrometry, where reduced droplet size can yield improved precision and freedom from interferences.

Hydrodynamic Flow Patterns as a Simple Aid to Effective Inductively Coupled Plasma Torch Design

In the past 5 years interest has soared in the inductively coupled plasma (ICP) as an excitation source for optical emission spectrochemical analysis. As a result, the ICP has rapidly made the transition from research laboratory to industrial application facility and the number of ICP users has grown correspondingly. This report describes a simple yet effective technique to aid users in constructing, modifying, and repairing the most important component in their ICP system—the plasma torch.

Real-time, in-situ measurement of film thickness and uniformity during plasma ashing of photoresist

This paper will discuss the performance ofequipment which monitors and so controls photoresist thickness and uniformity during plasma ashing without interfering with the process. Practical monitoring of a subtractive process of this type is significantly more complex than monitoring deposition processes. An initial absolute thickness measurement is needed. In addition the device must view the layer through a luminous medium and cannot rely on simple optical interference fringe counting. The equipment is self-calibrating and sensitive to layers dnm thick. An application to partial plasma resist ashing in high uniformity equipment will be described. Application to other films (e. g. oxide) will be discussed.