Project #77519 - Wet Etching

Problem 2: (Wet Etching – 25 pts)

Aligning an optical fiber to the laser light source with less than 1 µm transverse error is a demanding task. V-grooved Silicon substrate has been developed to enable accurate and cost effective interconnection without the use of highly skilled labor and expensive fixtures.  The technology is available through the KOH bulk micromachining of the {100} silicon. The mechanical tolerances delivered can be tight with this method at a relatively low processing cost. Assume that the diameter of an optical fiber is 125 µm and that the fiber is aligned along the B-B’ direction of the groove. The cross sectional shape of the groove along A-A’ is given in Figure 1. 

 

a)   The etch mask material is silicon nitride, which is better than silicon oxide in terms of dimensional accuracy of the V-groove. If the center of the fiber core is located exactly on the surface plane of the silicon, what is the depth of the V-groove, h, and width of the groove opening, w?

b)  Assume the KOH solution etches the (100) silicon at 2 µm/min and the thickness of the wafer is 500 µm. What will be the etching time needed for the V-groove in Fig. 1?

c)  Assuming that the nitride etch rate is 10,000 times slower than Si, what should the nitride layer thickness be in order to etch this groove accurately? Repeat the calculation with an oxide layer assuming that etches only 100 times slower than Si.

d) If we now want to collimate light coming out of this fiber, a ball lens can be placed in front of the fiber. A trihedral hole would be a good fixture for this spherical ball lens. Can you suggest a way to manufacture a trihedral hole using wet etching of either (100) or (110) Silicon?

 

 

Subject Science
Due By (Pacific Time) 07/27/2015 04:00 am
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