GaN Substrate Treatment for Si Impurity Control
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Solution Overview
Problem
Existing methods for treating group III nitride substrates before growing a group III nitride crystal result in the formation of high-concentration Si impurity layers, leading to suboptimal device characteristics, particularly in n-type carrier control, due to residual abrasive grains and diffusion during heat treatment, which degrades the flatness and performance of electronic devices like LEDs.
Innovation Solution
A method involving chemical mechanical polishing (CMP) followed by heat treatment in a nitrogen gas atmosphere and subsequent annealing in a mixed gas of hydrogen and nitrogen, or hydrogen and ammonia, to suppress Si impurity layer formation, ensuring a clean substrate for epitaxial growth and improving device characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If heat treatment is performed at 1100°C or higher for 10 minutes or more to remove Si impurity layer, then Si impurity concentration is reduced, but surface flatness deteriorates
Solution Approach 1:
The invention changes the heat treatment parameters by performing treatment at a lower temperature (900-1100°C) for a longer duration (30-120 minutes) in a nitrogen atmosphere, rather than at higher temperatures for shorter times. This parameter optimization reduces Si impurity concentration while preserving surface flatness by avoiding excessive thermal energy that would cause surface degradation.
Solution Approach 2:
The invention introduces a nitrogen atmosphere as an inert environment during heat treatment. This prevents oxidation and other harmful reactions on the GaN substrate surface while allowing controlled diffusion processes to occur. The nitrogen atmosphere protects the surface flatness while still enabling Si impurity removal through controlled diffusion into the bulk material.
2Shape
If CMP process is applied to achieve flat surface, then surface flatness is improved, but Si impurity layer is formed at interface
Solution Approach 1:
The invention extracts or removes the harmful Si impurity layer that forms during CMP by performing subsequent heat treatment. The heat treatment causes Si atoms to diffuse from the surface into the bulk material or to be removed through surface reactions, effectively extracting the contaminant while preserving the flat surface morphology achieved by CMP.
Solution Approach 2:
The invention converts the harmful Si impurity layer formed during CMP into a beneficial process by using controlled heat treatment to redistribute the Si atoms. The Si impurities are diffused into the bulk material where they become less harmful, or are converted into beneficial surface modifications, thereby transforming the CMP defect into an opportunity for controlled material engineering.
3Manufacturing precision
If heat treatment is performed to remove affected layer, then Si impurity layer is removed, but flatness obtained through CMP deteriorates
Solution Approach 1:
The invention optimizes heat treatment parameters by using moderate temperatures (900-1100°C) extended durations (30-120 minutes) in nitrogen atmosphere. This parameter set allows sufficient time for Si impurity diffusion and removal while avoiding the excessive thermal energy that would cause surface flatness deterioration. The extended lower-temperature treatment is gentler on the surface than brief high-temperature treatment.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed method effectively reduces Si impurity concentrations near the interface, enhancing the breakdown voltage and reverse leakage current of electronic devices, achieving characteristics superior to those obtained with conventional methods.
Implementation Method 1
a high-concentration Si impurity layer exists at an interface between a GaN layer and a GaN substrate... abrasive grains (colloidal silica), which have adhered to the surface of a GaN substrate in CMPing the surface before the formation of a GaN layer and have not been completely removed after the subsequent cleaning process to remain as particles on the affected layer formed on the surface of the GaN substrate, and deposits, which have volatilized from a case or the like to adhere to the surface of the GaN substrate while a GaN substrate has been stored, diffuse when it is heated to have an elevated temperature in GaN layer formation
Implementation Method 2
the GaN substrate is heat-treated at a temperature of 1100°C or higher for 10 minutes or more under the atmosphere of a process gas containing ammonia and hydrogen in a MOCVD apparatus
Implementation Method 3
Chemical mechanical polishing (CMP) is typically applied as the method for treating a GaN substrate surface, which is performed prior to layer lamination
Implementation Method 4
subsequent annealing in a mixed gas of hydrogen and nitrogen, or hydrogen and ammonia, to suppress Si impurity layer formation
Data Source
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AI summary
Provided is a method for treating a group III nitride substrate capable of obtaining, in the case where a group III nitride layer is laminated thereon, a group III nitride substrate that can form an electronic device having excellent characteristics. The method for treating a group III nitride substrate includes the steps of CMPing a surface of a substrate, elevating a temperature of the group III nitride substrate after the CMP process to a predetermined annealing temperature under a nitrogen gas atmosphere, and holding the group III nitride substrate whose temperature has been elevated to the annealing temperature for four minutes or more and eight minutes or less in a first mixed atmosphere of a hydrogen gas and a nitrogen gas or a second mixed atmosphere of a hydrogen gas and an ammonia gas.