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8 III-Nitride LED Chip Fabrication Techniques
8.3.1 Etching Parameters
• Etch rate
Etching speed refers to the materials removed per unit time from the etched surface
of the silicon wafer.
• Uniformity
Uniformity in etching includes both the uniformity of the entire surface and the lateral
erosion of the sidewalls.
• Etch selectivity ratio
The etch selectivity ratio is defined as the ratio of the etch rate of the etched material
to the etch rate of the mask material. The etching option can be calculated by the
following formula 8.1:
S = D/d
(8.1)
where S is the etching selectivity ratio, D is the etching depth of the material to be
etched per unit time, sand d is the etching depth of the mask material per unit time.
In order to fully transfer the pattern onto the material to be etched, it is necessary to
select an etching process and a mask material with a high etching selectivity.
8.3.2 Wet Etching and Dry Etching
Wet etching is a technique in which an etching material is immersed in an etchant for
corrosion. A specific chemical solution is used to dissolve a material. Wet etching
is a purely chemical process that leads to an isotropic sidewall morphology and the
high selectivity. Wet etching is divided into three basic steps: corrosion, cleaning,
and drying.
Wet etching is a traditional process that has been widely used in IC manufacturing
at feature sizes greater than 3 microns. It has been replaced by dry (plasma) etching
in the etching of passivation layer (SiO 2 ) in LED fabrication as well as in some
un-patterned film removal, such as the removal of silicon nitride and titanium. Wet
etching is also used to remove metal layers during rework experiments.
Dry etching is a technique of performing plasma etching using plasma. The highfrequency RF is used to activate the reaction gas into active ions, where they react
with the materials to be etched to form a volatile product and are removed. It has
the advantage of a fast etch rate while achieving good physical topography. The
characteristics of dry etching are high resolution and strong anisotropy. Dry etching
is further divided into physical etching (sputter etching IBE), chemical etching (or
8 III-Nitride LED Chip Fabrication Techniques
8.3.1 Etching Parameters
• Etch rate
Etching speed refers to the materials removed per unit time from the etched surface
of the silicon wafer.
• Uniformity
Uniformity in etching includes both the uniformity of the entire surface and the lateral
erosion of the sidewalls.
• Etch selectivity ratio
The etch selectivity ratio is defined as the ratio of the etch rate of the etched material
to the etch rate of the mask material. The etching option can be calculated by the
following formula 8.1:
S = D/d
(8.1)
where S is the etching selectivity ratio, D is the etching depth of the material to be
etched per unit time, sand d is the etching depth of the mask material per unit time.
In order to fully transfer the pattern onto the material to be etched, it is necessary to
select an etching process and a mask material with a high etching selectivity.
8.3.2 Wet Etching and Dry Etching
Wet etching is a technique in which an etching material is immersed in an etchant for
corrosion. A specific chemical solution is used to dissolve a material. Wet etching
is a purely chemical process that leads to an isotropic sidewall morphology and the
high selectivity. Wet etching is divided into three basic steps: corrosion, cleaning,
and drying.
Wet etching is a traditional process that has been widely used in IC manufacturing
at feature sizes greater than 3 microns. It has been replaced by dry (plasma) etching
in the etching of passivation layer (SiO 2 ) in LED fabrication as well as in some
un-patterned film removal, such as the removal of silicon nitride and titanium. Wet
etching is also used to remove metal layers during rework experiments.
Dry etching is a technique of performing plasma etching using plasma. The highfrequency RF is used to activate the reaction gas into active ions, where they react
with the materials to be etched to form a volatile product and are removed. It has
the advantage of a fast etch rate while achieving good physical topography. The
characteristics of dry etching are high resolution and strong anisotropy. Dry etching
is further divided into physical etching (sputter etching IBE), chemical etching (or