8.3 Etching Process
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two most important performance indicators for ITO films are resistivity and light
transmission. The etch rate of ITO is usually low with ICP dry etching. Usually, ICP
etching rate for ITO is 20 nm/min or so. Therefore, the common method to etch ITO
is to use wet etching. The ITO etching solution (mainly composed of hydrochloric
acid and ferric chloride solution) has a higher etching rate of the ITO transparent
conductive film. The cost of wet etching is also lower than that of the ICP dry etching.
The silicon dioxide (SiO 2 ) is a mask material and also a passivation layer
commonly used in the LED chip manufacturing process. The SiO 2 mask is etched
during the pattern transfer process. When the quality of the edge of the pattern is not
high, the SiO 2 may be etched off by a wet etching technique. A commonly used wet
etchant for SiO 2 is an HF solution. In order to reduce the penetration of hydrofluoric
acid on the photoresist during wet etching and to avoid the loss of hydride, NH 4 F can
be used as a buffer. The HF solution added with NH 4 F is called buffered oxidation
etchant (BOE) solution.
Compared with the wet etching of SiO 2 with BOE solution, RIE dry etching can
provide higher etching precision and ensure the flatness of the etched edge. The
commonly used etching gases are SF 6 and CHF 3, etc., which are chemically reacted
by active particles (F) and SiO 2 in the plasma to produce volatile etching products
for etching. When the SiO 2 mask is etched by CHF 3 /Ar mixed gas, CHF 3 can not
only produce active radicals (F) to chemically etch SiO 2 , but also can be used as a
passivating agent. The exposed sidewalls are protected after etching to ensure that the
sidewalls are steep, and the Ar ions bombard the SiO 2 to cause physical sputtering.
After the dry etching process is completed, the SiO 2 mask material is removed using
a BOE solution.
8.4 Evaporation and Sputtering
The evaporation process refers to depositing one or more layers of ITO transparent
electrodes and metals such as Cr, Ni, Pt, Au, etc. on the surface of the wafer. In
general, the wafer is loaded into a vacuum chamber under a high temperature and
metal is deposited on the wafer. In the production of LED chips, an electrode is
deposited on the wafer by an evaporation process. The current conducting area of
the wafer is increased by vapor deposition of metal layer.
8.4.1 Metal Evaporation
The evaporator is mainly divided into a thermal evaporation and an electron beam
evaporation according to the energy source. In view of the high melting point of
the metal as the electrode and the requirement of metal adhesion, the electron beam
evaporation machine (E-beam evaporator) is commonly used in the LED industry.
At present, the evaporator for LED production in China is still mainly imported.
161
two most important performance indicators for ITO films are resistivity and light
transmission. The etch rate of ITO is usually low with ICP dry etching. Usually, ICP
etching rate for ITO is 20 nm/min or so. Therefore, the common method to etch ITO
is to use wet etching. The ITO etching solution (mainly composed of hydrochloric
acid and ferric chloride solution) has a higher etching rate of the ITO transparent
conductive film. The cost of wet etching is also lower than that of the ICP dry etching.
The silicon dioxide (SiO 2 ) is a mask material and also a passivation layer
commonly used in the LED chip manufacturing process. The SiO 2 mask is etched
during the pattern transfer process. When the quality of the edge of the pattern is not
high, the SiO 2 may be etched off by a wet etching technique. A commonly used wet
etchant for SiO 2 is an HF solution. In order to reduce the penetration of hydrofluoric
acid on the photoresist during wet etching and to avoid the loss of hydride, NH 4 F can
be used as a buffer. The HF solution added with NH 4 F is called buffered oxidation
etchant (BOE) solution.
Compared with the wet etching of SiO 2 with BOE solution, RIE dry etching can
provide higher etching precision and ensure the flatness of the etched edge. The
commonly used etching gases are SF 6 and CHF 3, etc., which are chemically reacted
by active particles (F) and SiO 2 in the plasma to produce volatile etching products
for etching. When the SiO 2 mask is etched by CHF 3 /Ar mixed gas, CHF 3 can not
only produce active radicals (F) to chemically etch SiO 2 , but also can be used as a
passivating agent. The exposed sidewalls are protected after etching to ensure that the
sidewalls are steep, and the Ar ions bombard the SiO 2 to cause physical sputtering.
After the dry etching process is completed, the SiO 2 mask material is removed using
a BOE solution.
8.4 Evaporation and Sputtering
The evaporation process refers to depositing one or more layers of ITO transparent
electrodes and metals such as Cr, Ni, Pt, Au, etc. on the surface of the wafer. In
general, the wafer is loaded into a vacuum chamber under a high temperature and
metal is deposited on the wafer. In the production of LED chips, an electrode is
deposited on the wafer by an evaporation process. The current conducting area of
the wafer is increased by vapor deposition of metal layer.
8.4.1 Metal Evaporation
The evaporator is mainly divided into a thermal evaporation and an electron beam
evaporation according to the energy source. In view of the high melting point of
the metal as the electrode and the requirement of metal adhesion, the electron beam
evaporation machine (E-beam evaporator) is commonly used in the LED industry.
At present, the evaporator for LED production in China is still mainly imported.