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8 III-Nitride LED Chip Fabrication Techniques
When the temperatures of brighteners is higher than 25 °C, the cathodic polarization
drops significantly. When the temperature exceeds 35 °C, the coating is completely
darkened. The temperature is generally controlled at 5–25 °C. Increased operating
temperatures, high copper sulfate concentration and agitation can increase the allowable cathode current density. In the normal current density range, the higher the
current density is, the larger the deposition rate is. This can also improve the brightness and flatness of the plating layer. In bright acid copper plating, electrolytic copper
is generally not used, and a copper anode containing phosphorus is used. This is
because cuprous oxide is easily generated on the surface when an electrolytic copper
anode is used. The consumption of the brightener will increase, and the quality of
the plating layer is reduced. In order to avoid the generation of copper powder and
monovalent copper ions, a copper anode containing 0.04–0.3% of phosphorus should
be used.
8.7.2 Bonding Technology
Bonding technology refers to the bonding of two wafers, where the surface is clean
under certain conditions, by chemical bonding of the surface directly or through the
bonding material of the intermediate layer. Bonding techniques are not limited by
the lattice or crystal orientation of the two wafer materials. Therefore, the use of
bonding technology to combine new structural materials has great freedom. It can
also better utilize the different electrical and optical properties of various materials,
and provides a broader design space for device design.
At present, bonding technology has been widely used in the field of SOI material
preparation, microelectronic technology, sensor technology, MEMs, optical devices
and so on. At present, the bonding technology can be divided into multiple bonding
technologies, medium bonding technology, low temperature eutectic bonding technology and so on. From the technical point of view, the bonding technology can
be divided into two categories: direct bonding and bonding layer bonding. Different
types of bonding technologies have their unique applications in their respective fields.
The introduction of bonding technology into the substrate transfer technology of
GaN-based LED epitaxial wafers based on sapphire substrates is a very suitable
solution for fabricating GaN-based vertical structure LEDs.
It is difficult to bond GaN crystal directly to other materials without passing
through the intermediate adhesion layer. The choice of bonded substrate material
depends mainly on its electrical conductivity, thermal conductivity, and degree of
thermal mismatch with GaN materials. It is currently difficult to find a substrate
material that is thermally matched with GaN. Si and Cu are good choices in terms of
conductivity, thermal conductivity, and cost. Currently, there are GaN-based vertical
structure LED products based on these two materials.
Hot-temperature metal bonding is a bonding technique suitable for fabricating
GaN-based vertical structure LEDs: first, a bonding metal layer is deposited on the
epitaxial wafer and the surface of the substrate material. Under a certain temperature,
8 III-Nitride LED Chip Fabrication Techniques
When the temperatures of brighteners is higher than 25 °C, the cathodic polarization
drops significantly. When the temperature exceeds 35 °C, the coating is completely
darkened. The temperature is generally controlled at 5–25 °C. Increased operating
temperatures, high copper sulfate concentration and agitation can increase the allowable cathode current density. In the normal current density range, the higher the
current density is, the larger the deposition rate is. This can also improve the brightness and flatness of the plating layer. In bright acid copper plating, electrolytic copper
is generally not used, and a copper anode containing phosphorus is used. This is
because cuprous oxide is easily generated on the surface when an electrolytic copper
anode is used. The consumption of the brightener will increase, and the quality of
the plating layer is reduced. In order to avoid the generation of copper powder and
monovalent copper ions, a copper anode containing 0.04–0.3% of phosphorus should
be used.
8.7.2 Bonding Technology
Bonding technology refers to the bonding of two wafers, where the surface is clean
under certain conditions, by chemical bonding of the surface directly or through the
bonding material of the intermediate layer. Bonding techniques are not limited by
the lattice or crystal orientation of the two wafer materials. Therefore, the use of
bonding technology to combine new structural materials has great freedom. It can
also better utilize the different electrical and optical properties of various materials,
and provides a broader design space for device design.
At present, bonding technology has been widely used in the field of SOI material
preparation, microelectronic technology, sensor technology, MEMs, optical devices
and so on. At present, the bonding technology can be divided into multiple bonding
technologies, medium bonding technology, low temperature eutectic bonding technology and so on. From the technical point of view, the bonding technology can
be divided into two categories: direct bonding and bonding layer bonding. Different
types of bonding technologies have their unique applications in their respective fields.
The introduction of bonding technology into the substrate transfer technology of
GaN-based LED epitaxial wafers based on sapphire substrates is a very suitable
solution for fabricating GaN-based vertical structure LEDs.
It is difficult to bond GaN crystal directly to other materials without passing
through the intermediate adhesion layer. The choice of bonded substrate material
depends mainly on its electrical conductivity, thermal conductivity, and degree of
thermal mismatch with GaN materials. It is currently difficult to find a substrate
material that is thermally matched with GaN. Si and Cu are good choices in terms of
conductivity, thermal conductivity, and cost. Currently, there are GaN-based vertical
structure LED products based on these two materials.
Hot-temperature metal bonding is a bonding technique suitable for fabricating
GaN-based vertical structure LEDs: first, a bonding metal layer is deposited on the
epitaxial wafer and the surface of the substrate material. Under a certain temperature,