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Use of anisotropic wet etching and high rate RIE etching to fabricate precision silicon optical benches

IP.com Disclosure Number: IPCOM000019627D
Original Publication Date: 2003-Sep-23
Included in the Prior Art Database: 2003-Sep-23
Document File: 3 page(s) / 121K

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An improved method of forming a precision Silicon optical bench is disclosed where by using anisotropically wet etched features having the same maximum dimensions along with deep Si RIE to connect the wet etched features and a customized layer over the features on which the ball lens or optical fibers rest, the need to precisely align the anisotropic wet etching mask to the Si crystallographic direction can be relaxed.

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  Use of anisotropic wet etching and high rate RIE etching to fabricate precision silicon optical benches

  For optical communications, it is necessary to precisely align (to a fraction of a micron) passive optical components such as optical fibers and ball lens. This is typically done using a Silicon optical bench (SiOB) where anisotropically etched features are formed to hold the passive components. Anisotropic etching offers the unique advantage of enabling precise height control for cylindrical or spherical objects by controlling the lateral dimensions of the etched features. One difficulty of anisotropic etching is that convex corners require the use of complicated corner compensation structures which are often difficult to implement in practice. Convex corners are necessary to form a clear optical path connecting the features containing the passive optical components. The use of high etch rate reactive ion etching (RIE) in addition to anisotropic wet etching can enable a SiOB design which avoids corner compensation structures and has only rectangular shapes for anisotropic etching, which are self terminating. An additional difficulty in forming a precision SiOB is the requirement that the mask used to define the features to be anisotropically etched must be precisely aligned with the Si crystallographic directions. If the mask is not correctly aligned, the etched features will be larger then expected as shown in Fig. 1 for a square feature.

Fig. 1 0For example, with a 1 mm square pit for a ball lens, an 0.02 rotation error will increase the feature size by 0.35 microns which would cause the ball lens to be 0.25 microns lower than expected. The typical solution is to expose and etch an "alignment pattern" as an initial step to determine the location of the (110) Si planes and to create alignment marks, but this requires additional processing steps and can be difficult to implement with the necessary precision. Disclosed is an alternate design method and process which reduces the precision with which the anisotropic wet etching mask needs to be aligned to the Si crystallographic direction.

The disclosed solution is to form all of the anisotropically etched features for locating the passive components with...