Over-etching

Heat scales and mst on steel are not of even composition or thickness, and parts are subject to uneven pickling. To minimize over-etching, inhibitors are sometimes used to slow the attack on the clean steel. Many inhibitors produce strong adverse effects if carried into the plating solution. A second electrocleaning step is used after the pickle when inhibitors are employed. 

When plating any substrate less noble than copper, only a few mg/L of dissolved copper in the acid baths can adversely affect adhesion. Coatings can be too thin to be visible, yet contribute to poor adhesion. Small additions of thiourea have been used to prevent copper immersion, but it acts as a potent inhibitor, and work should be re-electrocleaned after the acid. Work should be exposed to the mildest acid treatments possible. Over-etching should be avoided. 

In addition to inspecting for possible contamination, it usually is also of interest to determine whether the chemical etching or anodization process has actually produced the desired oxide. For this purpose, anodization has somewhat of an advantage over etching (FPL, for example) because the thicker oxide developed... 

It cannot be emphasized enough that the determination of the contact resistance is not a trivial matter. First, a decision about what measuring structure must be made (four terminal Kelvin, sheet end or other structures) and what correction factors for the current crowding will have to be used. Then extreme care should be taken such that no over etching of the contact down into the silicon occurs and that the correct contact size is... 

At certain areas of the wafer (where the thinnest film coincides with the fastest etch rate) all these effects will work together giving a total plug over etch of at least 150 nm. Since we also have to include loading effects (see back etch) we come close to what was allowed in the example above (that was 0.2 nm recess). (+/-10% thickness or etch rate spread means a standard deviation of about 3%.)... 

Structure is shown that is suspended over etched features on Si substrate. 

Fig. 5 (A) Depicts wafer prior to etching and (B) depicts the result of etching to endpoint. Removing the remainder of film 2 (residue) requires over-etching of both the wafer and film 1.

Due to non-uniformity of the poly silicon layer across the wafer, twice as much time may be required to clear polysilicon from all umnasked regions. To restrict destruction of the thin oxide layer dnring the over-etching, another selectivity criterion should be satisfied ... 

Figure 12. Optical photograph of a stained cleavage edge of VPE InP grown over etched "dovetails along [Oil] direction in (100) InP.

A fine Ge line of 7 nm width was made from 10 nm width MC6AOAc resist pattern (5). The smoothness of the resist side wall enables the line width to be narrowed by over-etching. Making of A1 lines was also demonstrated (6). 

Applications that require precise etching of DEC conductors must be chosen considering the fact that the etching process is lateral as well as vertical. The result is that the etchant has a tendency to produce finer traces than the photomask used due to this lateral etching. An etch-back factor, which is often determined experimentally for a given etching system, is normally used to expand the artwork to account for this over-etch. 

Power level Is set, determined by power density required during material-specific qualifying trial activity. Web speed, electrode width, number of sides treated, and power density directly determine the required station power (Watt). Supplying no more than the maximum rated number of Watts per foot (or meter) of electrode length prevents potential surface overtreatment effects, such as over-etching, and can prevent electrode over-heating. 

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