When silicon is anisotropically etched, the etch rate of individual crystal planes of silicon is different from one another. Therefore, corner undercutting in KOH solution is critical and it is difficult to form full convex corners without compensation. Consequently, an abnormal square structure can be generated, which affects the operation characteristics of elements.
In the fabrication of diaphragms for a pressure sensing unit with square-shaped convex corners, compensation patterns should be arranged in each corner so that the beam part, where resistances are set up, is not changed by etching.
Several compensation methods have been used to solve this problem. Triangular, square and banded compensation patterns have been widely used to protect rectangular edges and these are now recognized to be classic compensation methods.
However, general principles to design individual compensation structures and compensation patterns, especially formulae to determine the dimension of compensation patterns do not seem to be introduced in detail.
Jon Chung Hyok, a researcher at the Faculty of Semiconductor Institute, has proposed a method to determine the shape and dimension of reasonable compensation patterns to make very thin diaphragms from 10~15㎛ to 250~300㎛ in thickness with square mass.
First, for fabrication of V-grooves structures with mass by corner compensation, he showed the compensation mechanism by several compensation patterns. The experiments on different types of compensation patterns showed that a diagonal-type compensation pattern is the best in performance. However, when etching depth should be ranged from 150㎛ to 200㎛, this compensation pattern is not suitable for compensation because the dimension of the mass and diaphragm should be restricted along their edges.
Next, on the analysis of the experimental results, he determined conditions for V-grooves structure from the given compensation pattern.
He concluded that when two types of compensation patterns are combined, the dimension of a square compensation pattern should be calculated before compensated corners with band compensation patterns are used to satisfy the insufficient etching depth, in order to increase the compensation effect.
Subsequently, he has made a diaphragm with the mass where a/h is less than 3.72 and b/h is less than 3.33 by applying corner compensation patterns.
More information about this is found in his paper “V-grooves Structures of Semiconductor Pressure Sensors with mass by Convex Corner Compensation” published in “Journal of Analog and Digital Devices” (EI).
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