160
8 III-Nitride LED Chip Fabrication Techniques
the production requirements. Due to the above reasons, the wet etching technique
has not been applied to the etching of GaN materials.
At present, among the group III nitride LEDs, dry etching is mainly used. The
GaN material is etched by the inductively coupled plasma (ICP) technology by using
a Cl 2 /BCl 3 mixed gas. There are complex chemical etching processes and physical
sputtering processes in the ICP etching process. The chemical etching process is a
chemical reaction between the active particles and the surface of the material to be
etched. The chemical process mainly consists of two parts.
First, when the Cl 2 /BCl 3 mixed gas enters the reaction chamber of the ICP etcher,
plasma is generated under the action of the RF electric field. The etching gas is
decomposed into various neutral particles, electrons (e), and active free radicals
(Cl, BCl), positively cssharged ions (Cl
+
2 , Cl
+ , BCl
+
2 ) and negatively charged ions
(sCl
− ). The second major reaction of the chemical process is the interaction of these
active particles with the solid surface of the substrate, that is, the etching process
is a chemical reaction process at the interface between the gas phase and the solid
phase. The positively charged ions under the acceleration electric field bombard the
GaN surface of the material, forming the physical sputtering bombardment. While
the active particles are adsorbed on the GaN surface of the material, the chemical
reaction with GaN can form volatile substance (generating material GaCl x ) that is
pumped out from the reaction chamber through the pumping system. In the formation
of the Cl 2 /BCl 3 ions, the neutral group plays a major chemical role. It is generally
believed that the reaction product of Cl in GaN etching process is as follows.
GaN + Cl → Ga, GaCl x , Ga + GaCl x + N 2 (x = 1, 2, 3)
(8.2)
The main physical sputtering process during the etching process is that high energy
ions bombard the surface of the etched material to cause the surface material to be
sputtered. In the ICP etching process, the physical bombardment effect is not equivalent to the pure physical process in sputter etching. It has the function of breaking the
chemical bond between atoms, increasing the adhesion, accelerating the desorption
of the reactants, and promoting the engraving. It can also enhance the chemical reaction on the surface of the etched material and the desorption of non-volatile products
attached to the surface of the etched material. Since ion bombardment has a certain
amount of energy, it will cause damage to the material to be etched. Therefore, how to
choose the appropriate ICP etching process parameters, which has a certain etching
rate and reduce the damage caused by etching on the quality of GaN crystal, is the
key to manufacture high performance LED chips.
8.3.4 Etching of ITO and SiO 2 Materials
Indium tin oxide (ITO) transparent conductive film has good electrical conductivity
and transparency. Compared with other transparent conductive films, ITO films have
good chemical stability, thermal stability, and graphic processing characteristics. The
8 III-Nitride LED Chip Fabrication Techniques
the production requirements. Due to the above reasons, the wet etching technique
has not been applied to the etching of GaN materials.
At present, among the group III nitride LEDs, dry etching is mainly used. The
GaN material is etched by the inductively coupled plasma (ICP) technology by using
a Cl 2 /BCl 3 mixed gas. There are complex chemical etching processes and physical
sputtering processes in the ICP etching process. The chemical etching process is a
chemical reaction between the active particles and the surface of the material to be
etched. The chemical process mainly consists of two parts.
First, when the Cl 2 /BCl 3 mixed gas enters the reaction chamber of the ICP etcher,
plasma is generated under the action of the RF electric field. The etching gas is
decomposed into various neutral particles, electrons (e), and active free radicals
(Cl, BCl), positively cssharged ions (Cl
+
2 , Cl
+ , BCl
+
2 ) and negatively charged ions
(sCl
− ). The second major reaction of the chemical process is the interaction of these
active particles with the solid surface of the substrate, that is, the etching process
is a chemical reaction process at the interface between the gas phase and the solid
phase. The positively charged ions under the acceleration electric field bombard the
GaN surface of the material, forming the physical sputtering bombardment. While
the active particles are adsorbed on the GaN surface of the material, the chemical
reaction with GaN can form volatile substance (generating material GaCl x ) that is
pumped out from the reaction chamber through the pumping system. In the formation
of the Cl 2 /BCl 3 ions, the neutral group plays a major chemical role. It is generally
believed that the reaction product of Cl in GaN etching process is as follows.
GaN + Cl → Ga, GaCl x , Ga + GaCl x + N 2 (x = 1, 2, 3)
(8.2)
The main physical sputtering process during the etching process is that high energy
ions bombard the surface of the etched material to cause the surface material to be
sputtered. In the ICP etching process, the physical bombardment effect is not equivalent to the pure physical process in sputter etching. It has the function of breaking the
chemical bond between atoms, increasing the adhesion, accelerating the desorption
of the reactants, and promoting the engraving. It can also enhance the chemical reaction on the surface of the etched material and the desorption of non-volatile products
attached to the surface of the etched material. Since ion bombardment has a certain
amount of energy, it will cause damage to the material to be etched. Therefore, how to
choose the appropriate ICP etching process parameters, which has a certain etching
rate and reduce the damage caused by etching on the quality of GaN crystal, is the
key to manufacture high performance LED chips.
8.3.4 Etching of ITO and SiO 2 Materials
Indium tin oxide (ITO) transparent conductive film has good electrical conductivity
and transparency. Compared with other transparent conductive films, ITO films have
good chemical stability, thermal stability, and graphic processing characteristics. The