1. Field of the Disclosure
The present invention relates generally semiconductor processing. More specifically, examples of the present invention are related to semiconductor processing of stacked integrated circuit systems.
2. Background
As integrated circuit technologies continue to advance, there are continuing efforts to increase performance and density, improve form factor, and reduce costs. The implementation of stacked three dimensional integrated circuits have been one approach that designers sometimes use to realize these benefits. The advances in wafer bonding with very precise alignments make it possible to fabricate stacked chips on wafer-level. The possible applications could include logic chip bonding to memory, image sensors, among others. This offers the advantage of smaller form factor, higher performance, and lower cost.
A key challenge when implementing stacked three dimensional complementary metal-oxide semiconductor (“CMOS”) image sensors, which continue to get smaller and faster, relates to switching noise between the stacked three dimensional integrated circuits. Switching noise can be of particular concern to image sensors packaged in through-silicon vias (“TSV”) technology. With such packages, a number of traces or signal lines are laid out on the bottom side of the package. These traces often connect vias on the outer perimeter to solder balls (pins) in the inner region. During sensor operation, if a pin switches rapidly between high low states, and its corresponding trace runs underneath a sensitive part of the image sensor (e.g., pixel array), then switching noise may be coupled into the image sensor circuitry. This coupled noise may degrade the quality or increase noise in the output image data. The noise contributed from a pin depends on the location of the trace, the run length below the image sensor, the frequency of the switching, and the current in the trace. However, the noise emanating from these traces can affect a portion of the image sensor and even potentially the whole image sensor.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.