8.2 Photolithography
157
• Pattern check
There will be development failure, poor exposure, uneven coating problems in
the lithography process. There are also problems such as misalignment overlap
and misalignment during exposure. Furthermore, scratches, pinholes, defects and
contaminants on the surface of the wafer itself are fatal to lithography. Lithography
is an accurate art that requires precise conditions and operations to achieve nearperfect graphics transfer. After each step, inspections are carried out. The wafers
pass the inspections can move into the next process. The unqualified wafers can be
re-processed for lithography steps. Through monitoring the pattern, the lithography
pass rate can be effectively improved.
• Cleaning
After the pattern transferred, the photoresist has completed its mission and needs to
be removed. There are two kinds of photoresist removal methods: wet method and
dry method. Traditional LED fabrication processes typically employ a wet chemical
process. The wet method uses a variety of acid-based solutions or organic solvents
to etch away the photoresist. The most common solvent is acetone, which dissolves
most of the photoresist. Dry method is to etch photoresist with an oxygen plasma
ashing (strong oxidizing ashing).
8.3 Etching Process
According to the pattern defined by the lithography process, the photoresist is used as
a protection layer to achieve the designed pattern on the photoresist to the underlying
materials. Etching process is generally divided into wet etching and dry etching.
In the LED chip manufacturing process, etching process is very important. Since
GaN materials are very stable at room temperature and have high corrosion resistance,
it is difficult to use wet etching at room temperature. Inductively Coupled Plasma
(ICP) etching is used for GaN materials. The following section describe some of the
basic parameters used in the etching process. The wet etching and the dry etching are
then introduced respectively. Finally, the etching of the GaN epitaxial layer, the ITO
transparent conductive film and the silicon dioxide (SiO 2 ) mask material involved
in the manufacturing process of the group III nitride LED chip is discussed. The
etching technique of the above materials is introduced below.
157
• Pattern check
There will be development failure, poor exposure, uneven coating problems in
the lithography process. There are also problems such as misalignment overlap
and misalignment during exposure. Furthermore, scratches, pinholes, defects and
contaminants on the surface of the wafer itself are fatal to lithography. Lithography
is an accurate art that requires precise conditions and operations to achieve nearperfect graphics transfer. After each step, inspections are carried out. The wafers
pass the inspections can move into the next process. The unqualified wafers can be
re-processed for lithography steps. Through monitoring the pattern, the lithography
pass rate can be effectively improved.
• Cleaning
After the pattern transferred, the photoresist has completed its mission and needs to
be removed. There are two kinds of photoresist removal methods: wet method and
dry method. Traditional LED fabrication processes typically employ a wet chemical
process. The wet method uses a variety of acid-based solutions or organic solvents
to etch away the photoresist. The most common solvent is acetone, which dissolves
most of the photoresist. Dry method is to etch photoresist with an oxygen plasma
ashing (strong oxidizing ashing).
8.3 Etching Process
According to the pattern defined by the lithography process, the photoresist is used as
a protection layer to achieve the designed pattern on the photoresist to the underlying
materials. Etching process is generally divided into wet etching and dry etching.
In the LED chip manufacturing process, etching process is very important. Since
GaN materials are very stable at room temperature and have high corrosion resistance,
it is difficult to use wet etching at room temperature. Inductively Coupled Plasma
(ICP) etching is used for GaN materials. The following section describe some of the
basic parameters used in the etching process. The wet etching and the dry etching are
then introduced respectively. Finally, the etching of the GaN epitaxial layer, the ITO
transparent conductive film and the silicon dioxide (SiO 2 ) mask material involved
in the manufacturing process of the group III nitride LED chip is discussed. The
etching technique of the above materials is introduced below.