SUMMARYSUMMARYSUMMARYSUMMARY

Ion bombardment control, Ion bombardment control, Thermal management,Thermal management, No Defects (pits or pillars) formation,No Defects (pits or pillars) formation, Profile controlProfile control Plasma repeatabilityPlasma repeatability Plasma uniformityPlasma uniformity Loading effectLoading effect Optimum process conditionsOptimum process conditions

Ion Bombardment ControlIon Bombardment ControlPhysical sputtering is due to cinetic energy of positive ions Physical sputtering is due to cinetic energy of positive ions which impinge the etched areas. This leads to which impinge the etched areas. This leads to positive effectspositive effects as:as: Anisotropic profiles,Anisotropic profiles,But this also may lead to But this also may lead to significant damagessignificant damages as: as: Rough surface morphology (pits formation)Rough surface morphology (pits formation) TrenchingTrenching Bad selectivity against mask and underlayersBad selectivity against mask and underlayers Non stoechiometric surfaces (impact on device Non stoechiometric surfaces (impact on device performance).performance).High density Plasma enhances chemical reaction and High density Plasma enhances chemical reaction and decreases RF bias. This leads to better etching efficiency while decreases RF bias. This leads to better etching efficiency while reducing the physical part of the etch mechanism.reducing the physical part of the etch mechanism.In Corial systems, a quartz plate (a few mm thick) covers the In Corial systems, a quartz plate (a few mm thick) covers the cathode. This insulating cover also decreases the ion energy cathode. This insulating cover also decreases the ion energy and reduces excessive damages to the GaN surface.and reduces excessive damages to the GaN surface.

Thermal ManagementThermal Management

Temperature control of substrate to etch leads to better process Temperature control of substrate to etch leads to better process control. This leads to control. This leads to positive effectspositive effects as: as: Better etch selectivity,Better etch selectivity, Stable etch rates as surface reaction kinetic is well Stable etch rates as surface reaction kinetic is well controlled.controlled.

Negative effectsNegative effects are: are: High temperature of substrate during etching leads to High temperature of substrate during etching leads to excessive loss of N2. That leaves strong n-types conductive excessive loss of N2. That leaves strong n-types conductive regions which affect multi layer epitaxy (regions which affect multi layer epitaxy (Review of Dry Etching Review of Dry Etching of GaN and Related Materialsof GaN and Related Materials).).

In Corial systems, the temperature control of substrates during In Corial systems, the temperature control of substrates during etching is performed using helium backside cooling and etching is performed using helium backside cooling and mechanical clamping.mechanical clamping.

Profile ControlProfile ControlDevice manufacturing may request vertical or tapered Device manufacturing may request vertical or tapered profiles according to applications and technologies.profiles according to applications and technologies.

Process must enable low mask erosion to achieve vertical Process must enable low mask erosion to achieve vertical profiles. Hard masks as Si3N4, SiO2 and Ni are good profiles. Hard masks as Si3N4, SiO2 and Ni are good candidates.candidates.

Negative slopes can be obtained with a specific cathode Negative slopes can be obtained with a specific cathode design and particular process conditions.design and particular process conditions.

Controlled PR Mask erosion enables tapered to almost Controlled PR Mask erosion enables tapered to almost vertical profiles (55° to 85°).vertical profiles (55° to 85°).

This process feature depends upon size of the substrate.This process feature depends upon size of the substrate.

Plasma RepeatabilityPlasma Repeatability

Plasma ignition has dramatic influence on Plasma ignition has dramatic influence on final GaN etching results.final GaN etching results.It is extremely important to ensure It is extremely important to ensure high high reproducibility of plasma ignitionreproducibility of plasma ignition..In Corial systems, the editable multi-step In Corial systems, the editable multi-step processes warrants the repeatability of processes warrants the repeatability of plasma ignition and, thereby, stable etch plasma ignition and, thereby, stable etch performance.performance.

Plasma UniformityPlasma Uniformity

In many cases, as the wafer size is 50 mm In many cases, as the wafer size is 50 mm diameter, batch loading is requested to achieve diameter, batch loading is requested to achieve high throughput. Consequently, high throughput. Consequently, good uniformity good uniformity accross the wafer and wafer to waferaccross the wafer and wafer to wafer is is required.required.In Corial ICP source, the large size of the source In Corial ICP source, the large size of the source ((Ø270 mmØ270 mm) and a carefull design of the coil ) and a carefull design of the coil terminations enable excellent GaN etch terminations enable excellent GaN etch uniformity.uniformity.

Loading EffectLoading EffectIn batch loading, the loading effect has to be In batch loading, the loading effect has to be considered. The considered. The etch rate decreasesetch rate decreases with the with the wafer size and the wafer size and the number of wafersnumber of wafers..

800800

400400

1/4 of wafer1/4 of wafer

Etch Rate (nm/mn)Etch Rate (nm/mn)

7 wafers7 wafers

Adequate Adequate adjustment of RF biasing versus ICP adjustment of RF biasing versus ICP powerpower to get smooth etched surfaces, to get smooth etched surfaces,

Control of wafer temperatureControl of wafer temperature by helium assisted by helium assisted heat exchange to maintain resist and device heat exchange to maintain resist and device integrity,integrity,

Control of the etchingControl of the etching profile by the flow rate of profile by the flow rate of polymerizing gas (CH4) in the process recipe,polymerizing gas (CH4) in the process recipe,

Repeatability of the etching results by a Repeatability of the etching results by a well well controlled plasma ignitioncontrolled plasma ignition using a multi-step using a multi-step approach,approach,

Uniform etching of a batch of seven 2” wafers Uniform etching of a batch of seven 2” wafers thanks to the thanks to the large size of the ICP sourcelarge size of the ICP source (Ø270 (Ø270 mm).mm).

RECAP of GaN PROCESSRECAP of GaN PROCESS