Donald C. Grant

Theory for Deadend Microfiltration

In this chapter, theories for deadend microfiltration are presented. The first part of the chapter focuses on the sieving or surface filtration mechanism, which is dominant when the particles are physically too large to pass through the pores of the filter medium. The primary goal is to predict the flux decline due to the buildup of the rejected particles on the membrane surface. We start with Darcy’s law for the relationship between flux and pressure drop across a cake layer and membrane in series. This relationship is used to describe transient cake buildup and flux decline for batch operation of deadend microfilters. The analysis is then extended to continuous operation of rotary drum vacuum filters.

Methodology for reducing process variability through in-situ production of positive photoresist developer

Process variability in a photolithographic process can arise from a number of sources including photoresist developer assay variation. A change in activity of only +/- 0.001 eq/l in a developer solution with a normality of 0.2624 eq/l can consume or exceed the allowable +/- 5.0% CD specification set by most fabs. This change, which represents a relative error (error/setpoint) at 3(sigma) or only +/- 0.4%, is typical of the allowable variability from developer suppliers. Developer production systems with tighter assay tolerances should reduce process variability and increase process robustness. This study compared the effectiveness of several control techniques for blending tetramethyl ammonium hydroxide (TMAH) developer. Techniques with feedforward and feedback control were investigated. An analysis of sources of error in developer blending systems indicated that feedforward techniques could not achieve the desired relative error of +/- 0.4%. An experimental study was undertaken to determine the relative error of three feedback control methods. The feedback techniques yielded considerably tighter assay control than that expected from the feedforward techniques. An analog setpoint control algorithm used with conductivity measurements provided more precise control than a discrete setpoint control algorithm. However, only feedback control with titration met the goal, achieving a relative error of only +/- 0.13% at 3(sigma) (+/- 0.00034 eq/l).

Identification and Removal of Storage Induced Particle Contamination on Silicon Wafer Surfaces

Control of contamination on the surface of wafers during the manufacture of state-of-the-art microcircuits is imperative if high yields are to be obtained. Hence, wafers are often cleaned using a modified RCA clean to remove organic, metallic and particle contamination prior to microcircuit manufacture. Recently, wafers obtained from a particular vendor were found to have heavy particle contamination after a modified RCA clean. The wafers were also found to have a hydrophobic surface indicating the presence of heavy organic contamination. Analysis of the wafer surface revealed that it was covered with film of a polydimethylsiloxane-like compound. The source of the compound was found to be a gasket in the storage boxes used to transport the wafers. This paper describes the methodology used to identify the source of the contaminant and the cleaning methods developed to eliminate the particle contamination which it caused.