The semiconductor technology is not only applied to the preparation of integrated circuits on substrates containing silicon, but also applicable to applications for commercial products containing non-silicon substrates. Examples of these applications include sensors for thin film strain gauges. Prior to the deposition of the pattern, in order to ensure the electrical insulation between the metal substrate and the circuit, at least an insulation layer is formed on the surface of the metal substrate at the area where the circuits are grown.
In the conventional art, during the deposition of the insulation layer, the substrates are positioned as closed as possible with each other so to increase the productivity and uniformity. During the growth of the pattern every substrate is placed side by side against other substrates. In addition, according to the physical characteristics as required, the figure of the substrate varies in a wide range. This includes high substrates (&gt;10 mm) and deep openings. These factors make it difficult for the insulation layer to be coated on the substrate with uniformity along the whole surface. Especially, the side planes of the substrate or the openings are least likely to be coated with the insulation layer.
After the insulation layer is prepared, wet etching is subsequently processed. During the etching, not only the resistance layer but also the surface of the metal substrate is exposed to the etching solution. Owing to the coupling effect, the etching efficiency of the noble components will be retarded, compared with the speed while it is not coupled, but the etching efficiency of the active components will be accelerated in comparison with the speed while it is not coupled. In this case, the resistor of the coupled assembly is a noble component and the substrate is an active component. The etching efficiency to the resistor layer will therefore be retarded or even ceased at much higher temperature. The adhesion of the photoresist to the underlying circuit film will then be severely influenced which can subsequently lead to poor pattern definition and process reproducibility. When photoresist peels, the etching will even be stopped. Furthermore, owing to the accelerated corrosion of the substrate, the geometric size of the substrate can not be maintained.
It is thus a need in the industry to have an improvement in the wet etching so that the etching ability of the etchant can be maintained while the corrosion to the substrate can be avoided.