GaN Multilayer Bonding on Si for High-Temperature Regrowth
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Solution Overview
Problem
The challenge is to form a semiconductor device with good characteristics using a nitride semiconductor containing Ga on a Si substrate with a (100) plane orientation, as existing adhesive layers cannot withstand high temperatures necessary for high-quality GaN regrowth and etching, leading to issues like meltback etching and reduced high-frequency characteristics.
Innovation Solution
A method involving bonding a Si substrate with a nitride semiconductor layer grown in the +c-axis direction using an AlN adhesive layer, followed by removing the other substrate and selectively regrowing n-type GaN, and forming electrodes for ohmic contact, while using an etching stop layer and buffer layers to manage thermal decomposition and crystal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing adhesive layers are used for bonding Si substrate and nitride semiconductor layer, then bonding can be achieved, but the adhesive layers cannot withstand high temperatures necessary for high-quality GaN regrowth and etching, leading to meltback etching and reduced high-frequency characteristics
Solution Approach 1:
An AlN adhesive layer is introduced as an intermediary between the Si substrate and the nitride semiconductor layer. This AlN adhesive layer serves as a thermal mediator that can withstand high temperatures (above 1000°C) required for GaN regrowth and etching processes, preventing meltback etching while maintaining bonding functionality. The AlN layer has both adhesive properties for bonding and high thermal stability for withstanding processing temperatures.
Solution Approach 2:
The invention changes the material parameter of the adhesive layer from conventional organic or oxide adhesives with low thermal stability to AlN (aluminum nitride) with high thermal stability. This parameter change enables the adhesive layer to withstand temperatures above 1000°C, allowing high-quality GaN regrowth and etching processes to be performed without causing meltback etching or degrading the adhesive layer.
2Reliability
If N-polar nitride semiconductor layer is used to reduce contact resistance and inhibit short channel effect, then high-frequency characteristics improve, but crystal-growth quality deteriorates with lower surface flatness and higher dislocation density
Solution Approach 1:
Instead of directly growing N-polar nitride semiconductor on Si substrate (which produces poor crystal quality), the invention inverts the approach by first growing high-quality Ga-polar nitride semiconductor on Si substrate, then bonding it to another substrate. This inversion allows obtaining both high crystal quality from Ga-polar growth and the desired N-polar characteristics for reduced contact resistance and inhibited short channel effect.
Solution Approach 2:
The invention segments the crystal growth and substrate bonding processes into separate steps. First, high-quality nitride semiconductor layers are grown on Si substrate with appropriate polarity. Then, these pre-grown layers are bonded to another substrate using the AlN adhesive layer. This segmentation allows optimization of crystal growth conditions independently from the final device structure requirements.
3Reliability
If GaN layer is regrown at high temperature to reduce contact resistance, then ohmic contact improves, but existing adhesive layers decompose and cause meltback etching
Solution Approach 1:
The AlN adhesive layer acts as a protective intermediary between the GaN layer and the environment during high-temperature regrowth. It prevents meltback etching by providing a stable interface that does not decompose at regrowth temperatures, allowing the GaN layer to be regrown at high temperature to improve ohmic contact without causing harmful etching effects.
Solution Approach 2:
The AlN adhesive layer is formed beforehand to provide thermal and chemical stability during subsequent high-temperature processing. This prior cushioning prevents meltback etching from occurring during GaN regrowth, as the AlN layer maintains structural integrity at temperatures that would otherwise cause decomposition and etching of the GaN layer.
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
This approach enables the formation of high-quality nitride semiconductor devices with reduced contact resistance and improved high-frequency characteristics on Si substrates, avoiding meltback etching and heat dissipation limitations, thus integrating nitride semiconductor devices with CMOS circuits effectively.
Implementation Method 1
bonding a substrate that has a main surface formed as a (100) plane of Si and another substrate that has a nitride semiconductor layer formed through crystal-growth of a nitride semiconductor containing Ga to each other in a +c-axis direction, in a state where a surface of the other substrate on which the nitride semiconductor layer is formed is on a side of the substrate; an adhesive layer forming step of forming an adhesive layer formed of AlN
Implementation Method 2
another substrate that has a nitride semiconductor layer formed through crystal-growth of a nitride semiconductor containing Ga
Implementation Method 3
forming a nitride semiconductor layer including a buffer layer, an element formation layer, and an etching stop layer in this order from below on the adhesive layer through crystal-growth in a +c-axis direction
Implementation Method 4
selectively regrowing n-type GaN, and forming electrodes for ohmic contact
Data Source
AI summary
After a nitride semiconductor layer is formed through crystal-growth of a nitride semiconductor containing Ga in a +c-axis direction on the other substrate, the other substrate on which the nitride semiconductor layer is formed is bonded to a substrate in a state where a surface on which the nitride semiconductor layer of the other substrate is formed is on the side of the substrate (a bonding step). This bonding is performed by bonding the surfaces to be bonded by a known direct bonding technology.