8.7 Vertical Structure LEDs
179
a. Deep etch isolation and sidewall insulation protection
The methods to isolate materials in microelectronics are laser grooving, plasma
etching, ion implantation to form isolated islands, and epitaxial self-isolation. In
the production of microelectronic devices, the individual devices must be isolated
from each other in order to eliminate punch through and parasitic effects. Such a
process is called the isolated pixels. By isolation, the individual pixels are fabricated
in isolated areas. After the completion of the pixels, it is necessary to interconnect with low-resistance metal wires in order to achieve the overall function. The
interconnection wires must have good contact with the pixels. In IC technology, the
integrated circuit is manufactured in three processes: isolation of the device, flow
of the device, and wiring. In general, there are three main methods for device isolation: p–n junction reverse isolation, dielectric isolation, and trench isolation [37–40].
Some commonly used MOS components (bipolar transistors, CMOS) usually use a
p–n junction isolation or oxidation process to form isolated islands in order to prevent
parasitic effects.
GaN-based III–V nitride wide-bandgap semiconductors play an important role in
the field of blue light and ultraviolet optoelectronics. They are also important materials for manufacturing high-temperature and high-power semiconductor devices.
GaN material is a direct bandgap material with a band gap from 0.7 to 6.2 eV range
in accordance with Al or In dopants [41]. The III–V nitride has high thermal stability
and chemical stability. On the other hand, it also brings great difficulties to the manufacturing process of the device. The isolation of conventional GaN-based devices can
be achieved by wet etching, dry etching, and ion implantation. However, wet etching
process has poor controllability, slow rate, and poor heterogeneity. This makes such
a process not an ideal method for device isolation. At present, the isolation of GaN
devices is mainly achieved by dry etching such as reactive ion etching (RIE), electromagnetic cyclotron resonance (ECR) and inductively coupled plasma (ICP) etching,
and so on.
To fabricate a high-voltage chip array, it is necessary to insulate the micro pixels
from each other. Therefore, the GaN epitaxial layer between the micro pixels must
be etched to the sapphire substrate. Unlike the mesa etching in conventional LED
chip, the etching depth is generally 1–1.5 micron. The whole GaN epitaxial material
thickness is 6–7 micron, it requires long ICP etching. This makes necessary not only
high selective etching ratio of the mask but also the optimum ICP etching conditions.
Since the entire epitaxial layer needs to be etched to the sapphire substrate, an etching
mask of 4-micron photoresist is far less than the value calculated from the etching
ratio of the materials. Because the etching ratio between SiO 2 and GaN is 1:1, it is
preferable to design composite layers consisting of SiO 2 and photoresist as a mask
for deep etching.
In the microelectronics process, the CVD film can offer both conformal and nonconformal coatings to cover the underlying pattern. However, the specific coverage
depends on the type of film, the type of reaction system, and the deposition conditions.
The conformal deposition means that the same thickness of film can be deposited
179
a. Deep etch isolation and sidewall insulation protection
The methods to isolate materials in microelectronics are laser grooving, plasma
etching, ion implantation to form isolated islands, and epitaxial self-isolation. In
the production of microelectronic devices, the individual devices must be isolated
from each other in order to eliminate punch through and parasitic effects. Such a
process is called the isolated pixels. By isolation, the individual pixels are fabricated
in isolated areas. After the completion of the pixels, it is necessary to interconnect with low-resistance metal wires in order to achieve the overall function. The
interconnection wires must have good contact with the pixels. In IC technology, the
integrated circuit is manufactured in three processes: isolation of the device, flow
of the device, and wiring. In general, there are three main methods for device isolation: p–n junction reverse isolation, dielectric isolation, and trench isolation [37–40].
Some commonly used MOS components (bipolar transistors, CMOS) usually use a
p–n junction isolation or oxidation process to form isolated islands in order to prevent
parasitic effects.
GaN-based III–V nitride wide-bandgap semiconductors play an important role in
the field of blue light and ultraviolet optoelectronics. They are also important materials for manufacturing high-temperature and high-power semiconductor devices.
GaN material is a direct bandgap material with a band gap from 0.7 to 6.2 eV range
in accordance with Al or In dopants [41]. The III–V nitride has high thermal stability
and chemical stability. On the other hand, it also brings great difficulties to the manufacturing process of the device. The isolation of conventional GaN-based devices can
be achieved by wet etching, dry etching, and ion implantation. However, wet etching
process has poor controllability, slow rate, and poor heterogeneity. This makes such
a process not an ideal method for device isolation. At present, the isolation of GaN
devices is mainly achieved by dry etching such as reactive ion etching (RIE), electromagnetic cyclotron resonance (ECR) and inductively coupled plasma (ICP) etching,
and so on.
To fabricate a high-voltage chip array, it is necessary to insulate the micro pixels
from each other. Therefore, the GaN epitaxial layer between the micro pixels must
be etched to the sapphire substrate. Unlike the mesa etching in conventional LED
chip, the etching depth is generally 1–1.5 micron. The whole GaN epitaxial material
thickness is 6–7 micron, it requires long ICP etching. This makes necessary not only
high selective etching ratio of the mask but also the optimum ICP etching conditions.
Since the entire epitaxial layer needs to be etched to the sapphire substrate, an etching
mask of 4-micron photoresist is far less than the value calculated from the etching
ratio of the materials. Because the etching ratio between SiO 2 and GaN is 1:1, it is
preferable to design composite layers consisting of SiO 2 and photoresist as a mask
for deep etching.
In the microelectronics process, the CVD film can offer both conformal and nonconformal coatings to cover the underlying pattern. However, the specific coverage
depends on the type of film, the type of reaction system, and the deposition conditions.
The conformal deposition means that the same thickness of film can be deposited