Edwin Jan Klein - Universiteit Twente

Chapter 5
1. Definition of the vertical tapers
2. Port waveguide definition
3. Resonator waveguide definition
4. Definition of the chromium heaters
5. Definition of the gold electrodes
Of these five steps, however, only the alignment of the second and the third layers is
critical. It is therefore possible to use a hybrid approach, using stepper as well as
contact lithography. With this hybrid approach only two stepper wafer exposures are
required per device. Using a total of four images on the reticle it is therefore possible
to create two unique device groups that each measure 10 by 10 mm instead of only
one of that size. The layout of the images on the stepper reticle is shown in Figure
5.16. Images 1 and 3 define the port waveguides and resonators of a device group that
contains several routers respectively. Images 2 and 4 are used for a device group that
contains several routers in addition to several types of test structures.
If in the original 5 mask exposure steps only step 2 and 3 use stepper litho then a
problem will occur since the stepper cannot align to the vertical taper structures
defined by the first exposure step. However, it is possible to do the reverse: aligning a
contact mask to structures defined with the stepper. An additional exposure step is
therefore added to create the exposure sequence written in Table 5.2.
Table 5.2. Mask exposure sequence. The router does not use vertical tapers.
Exposure step 2 is therefore left open for the router.
OADM Router
1 Stepper reticle, Image 5 Stepper reticle image 5
2 Contact mask, Vertical tapers --
3 Stepper reticle, Image 2 Stepper reticle, Image 1
4 Stepper reticle, Image 4 Stepper reticle, Image 3
5 Contact mask, Chromium heaters Contact mask, Chromium heaters
6 Contact mask, Gold leads Contact mask, Gold leads
a)
b)
Figure 5.17. Alignment markers in the reticle images help to align the contact mask.
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Alignment
markers