must be preserved at this first intermediate value is subsequently deposited a second koh etching stage makes it possible to increase the depth of the non masked patterns 3 4 these additional mask deposition and etching stages are repeated as many times as necessary in order to obtain all the patterns in the desired layout depending on the initial window of the patterns etching may extend as far as the junction of the 111 crystallographic planes as is the case for pattern 4 it is also possible as shown in fig3 a and 3 b to use a single etching mask associated with two chemical etching stages more precisely as shown in fig3 a there is an initial chemical etching stage in the presence of a mask 17 which makes it possible to define incipient patterns 18 20 including faces sloping along the 111 planes and flat areas parallel to the 100 planes subsequently the etching mask is removed and as shown in fig3 b a second chemical etching stage is performed typically using koh the incipient patterns 18 20 are then etched in accordance with the instructions in the document entitled u201c novel micro machine technology for multi level structures of silicon u201d by minhang dao xinxin li shaogun shen and hong shen published in sensors and actuators a63 1997 pages 217 to 221 this second etching stage uses the considerable etching selectivity along the 311 planes which exists in the area of the convex crests 21 that are formed in the area of the boundaries of.