GaN Template Substrate Stress Control
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Solution Overview
Problem
Streaked morphological abnormalities occur on device substrates during the fabrication of group 13 nitride devices, leading to defective chips and reduced productivity, and existing methods using low-temperature interlayers introduce crystal defects that hinder the production of high-quality devices.
Innovation Solution
A GaN template substrate is developed with a sapphire base substrate and a first GaN layer having intrinsic compressive stress greater than or equal to 260 MPa and high crystallinity, as measured by Raman spectroscopy, to suppress the occurrence of streaked morphological abnormalities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a low-temperature interlayer is introduced to prevent cracks in GaN films, then crack prevention is improved, but crystal defects are introduced that interfere with fabrication of high-quality devices
Solution Approach 1:
An AlN interlayer is introduced as a mediator between the sapphire substrate and the GaN film. This interlayer has a hexagonal crystal structure that matches GaN well, serving as an effective buffer that prevents cracks while minimizing crystal defects. The AlN layer acts as a transition medium that resolves the lattice mismatch and thermal expansion coefficient difference between sapphire and GaN, thereby preventing cracks without significantly degrading crystal quality.
Solution Approach 2:
The patent changes the material parameter of the interlayer from conventional low-temperature materials to AlN, which has superior lattice matching with GaN. By changing the material composition and crystal structure parameters, the interlayer can effectively prevent cracks through its hexagonal structure while maintaining high crystal quality for subsequent GaN film growth.
2Length of moving object
If GaN films are made thicker on sapphire substrate, then device functionality is improved, but crack occurrence increases
Solution Approach 1:
The AlN interlayer is formed in advance before depositing the GaN film. This preliminary action creates a stable foundation that can support thick GaN films without cracking. The interlayer is prepared first to establish proper lattice matching and stress distribution, enabling subsequent thick GaN film growth while preventing crack formation.
Solution Approach 2:
The AlN interlayer serves as a mediator that enables the deposition of thick GaN films on sapphire substrates. By providing a lattice-matched interface, it allows the GaN film to grow to greater thicknesses without the stress accumulation that would otherwise cause cracks in thicker films.
3Productivity
If conventional templates are used for device substrate fabrication, then productivity is maintained, but streaked morphological abnormalities occur that reduce chip quality
Solution Approach 1:
The patent uses a composite template structure consisting of sapphire substrate + AlN interlayer + GaN film. This composite structure combines the advantages of each material: sapphire provides mechanical strength and thermal stability, AlN provides lattice matching and crack prevention, and GaN provides the desired electrical and optical properties. This composite approach eliminates streaked morphological abnormalities while maintaining high productivity for device chip fabrication.
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 solution effectively prevents streaked morphological abnormalities on device substrates, thereby improving the manufacturing yield of LED and HEMT chips by ensuring high-quality GaN films with controlled stress and crystallinity.
Implementation Method 1
the first GaN layer has a compressive stress greater than or equal to 260 MPa, the compressive stress being intrinsic in an inplane direction
Implementation Method 2
the compressive stress and the crystallinity are values that can be quantified by Raman spectroscopy
Implementation Method 3
a full width at half maximum of a peak near a wavenumber of 568 cm−1 in a Raman spectrum is lower than or equal to 1.8 cm−1, the peak representing E2 phonons of GaN
Data Source
AI summary
A device substrate in which no streaked morphological abnormality occurs is achieved. A GaN template substrate includes: a base substrate; and a first GaN layer epitaxially formed on the base substrate, wherein the first GaN layer has a compressive stress greater than or equal to 260 MPa that is intrinsic in an inplane direction, or a full width at half maximum of a peak representing E2 phonons of GaN near a wavenumber of 568 cm−1 in a Raman spectrum is lower than or equal to 1.8 cm−1. With all of these requirements, a device substrate includes: a second GaN layer epitaxially formed on the first GaN layer; and a device layer epitaxially formed on the second GaN layer and made of a group 13 nitride.