Physics for Electronics Engineering: Unit I: Crystallography
Pattern Alignment
Definition, Example | Crystallography
Pattern alignment is a process in which the mask patterns is aligned along different crystallographic directions. It also refers to alignment of mask pattern with respect to the pattern that already exists on the wafer.
PATTERN
ALIGNMENT
Pattern
alignment is a process in which the mask patterns is aligned along different
crystallographic directions. It also refers to alignment of mask pattern with
respect to the pattern that already exists on the wafer.
If the mask pattern is perfectly aligned
with respect to the pre-etched pattern it is termed as perfect alignment. If it
is not perfectly aligned then it is known as misalignment.
In the fabrication of MEMS (Micro
Electro Mechanical System) components, Bulk and Surface micromachining
processes basically involves several processing steps. Photolithography is one
of the major steps. These involve transferring of required pattern on the
substrate from the photo mask.
The exact structure of the desired
pattern mainly depends on two things.
(i) How accurately the mask edge is
aligned with the wafer flat.
(ii) How accurately the wafer flat is
defined by the manufacturers. (Fig. 1.40).
Generally, (100), (110) and (111)
silicon wafers with different flat orientations such as <100>,
<110> and <111> are <110 and 11 a available in the market. These
are used to fabricate different types of MEMS structures on wafer surfaces. A
small degree of misalignment of the mask edge with the wafer flat results in
significant change in the final structure.
Example
Consider a photolithography process that
requires two layers of fabrication. The alignment marks used are a cross-type feature
in the first layer, and a square pattern in the second layer. When properly
aligned, the cross-type feature should fit inside the square pattern. (Fig.
1.41)
Physics for Electronics Engineering: Unit I: Crystallography : Tag: : Definition, Example | Crystallography - Pattern Alignment
Physics for Electronics Engineering: Unit I: Crystallography
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Physics for Electronics Engineering
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