Planar device microfabrication

Figure 10.3 Schematic diagram of planar device microfabrication (in transverse section) (a and e) Si02 growth (b) AI2O3 wash coating (c and f) Pt deposition (d) black silicon formation [14].

Liang, Z., Chiem, N., Ocvirk, G., Tang, T., Fluri, K., Harrison, D.J., Microfabrication of a planar absorbance and fluorescence cell for integrated capillary electrophoresis devices. Anal. Chem. 1996, 68, 1040-1046. 

The chemical component of CMP slurry creates porous unstable oxides or soluble surface complexes. The slurries are designed to have additives that initiate the above reactions. The mechanical component of the process removes the above-formed films by abrasion. In most planarization systems the mechanical component is the rate-limiting step. As soon as the formed porous film is removed, a new one is formed and planarization proceeds. Therefore, the removal rate is directly proportional to the applied pressure. To achieve practical copper removal rates, pressures greater than 3 psi are often required. These pressures should not create delamination, material deformation, or cracking on dense or relatively dense dielectrics used in silicon microfabrication on conventional dielectrics. However, the introduction of porous ultra-low-fc (low dielectric constant) materials will require a low downpressure (< 1 psi) polishing to maintain the structural integrity of the device [7-9]. It is expected that dielectrics with k value less than 2.4 will require a planarization process of 1 psi downpressure or less when they are introduced to production. It is expected that this process requirement will become even more important for the 45-nm technology node [10]. 

Polymeric microfluidic systems coupled to a microfabricated planar polymer tip can be used as a stable ion source for ESI-MS. A parylene tip at the end of the microchannel delivers fluid which easily produces a stable Taylor cone at the tip via an applied voltage. The described device appears to facilitate the formation of a stable spray current for the electrospray process and hence offers an attractive alternative to previously reported electrospray emitters. When this interface was employed for the quantification of methylphenidate in urine extracts via direct infusion MS analysis, this system demonstrated stable electrospray performance, good reproducibility, a wide linear dynamic range, a relatively low limit of quantification, good precision and accuracy, and negligible system carryover. We believe polymeric devices such as described in this report merit further investigation for chip-based sample analysis employing electrospray MS in the future. 

The microfluidic device design and the relative flow rate of sheath and sample play important roles in hydrodynamic focusing. Lee et al. [6] proposed a theoretical model to predict the width of focused center flow inside a microfabricated flow cytometer [6]. Based on potential flow theory, they derived the equation for flow inside a planar microfabricated flow cytometer under the two-dimensional situation shown in Fig. 3a. The flow is considered laminar, and the diffusion and mixing between focused stream and sheath flows is assumed negligible. With these assumptions, conservation of mass yields... 

Liang Z et al (1996) Microfabrication of a planar absorbance and fluorescence cell fin integrated capillary electrophoresis devices. Anal Chem 68 1040-1046... 

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