Epitaxial GaN Growth via Temperature and Flow Rate Adjustment
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Solution Overview
Problem
The existing processes for growing nitride semiconductor layers, particularly GaN on an AlN layer, result in surface defects and pits due to lattice constant differences, leading to degraded crystal quality and device reliability, with thinner GaN layers exacerbating these issues and requiring thicker layers to compensate for surface imperfections.
Innovation Solution
A process involving the epitaxial growth of an AlN layer at a first temperature and flow rate of ammonia, followed by a GaN layer grown in two periods with a temperature and flow rate adjustment, allowing for continuous variation of growth conditions to match surface orientations and reduce defects and pits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a thinned AlN layer thinner than 50 nm is grown, then the crystal quality improves, but the layer grows in islands instead of a laminate structure inducing defects
Solution Approach 1:
The patent applies parameter changes by varying the ammonia flow rate and temperature during the GaN layer growth process. Specifically, the ammonia flow rate is adjusted from a first flow rate to a second flow rate, and the temperature is changed from a first temperature to a second temperature, which enables the GaN layer to grow in a laminate structure rather than islands, thereby reducing defects while maintaining thin AlN layer thickness.
2Reliability
If a thinned GaN layer is grown to enhance device performance, then pulse response improves, but the number of surface pits increases
Solution Approach 1:
The patent uses parameter changes during the GaN layer growth process, specifically adjusting the ammonia flow rate and temperature in two distinct periods. This controlled variation in growth parameters enables the formation of a high-quality GaN layer with reduced surface pits, allowing thin GaN layers to achieve both enhanced device performance and acceptable surface quality.
3Object-affected harmful factors
If a thickened GaN layer is grown to compensate for surface pits, then surface pit density decreases, but the device performance deteriorates
Solution Approach 1:
The patent resolves this contradiction by implementing a two-period growth process with controlled parameter changes. During the first period, the GaN layer is grown at a first temperature and ammonia flow rate, and during the second period, the parameters are adjusted to a second temperature and second ammonia flow rate. This enables the formation of a thin GaN layer with low surface pit density, achieving both good surface quality and high device performance without requiring excessive layer thickness.
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 effectively reduces surface pit density and improves crystal quality, enabling thinner GaN layers with enhanced performance and reliability, specifically achieving surface pit densities below 10/cm² with GaN layers thinner than 0.3 μm, thereby improving transistor pulse response.
Implementation Method 1
growing an aluminum nitride (AlN) layer at a first temperature and a first flow rate of ammonia (NH3); and growing a gallium nitride (GaN) layer on the AlN layer
Implementation Method 2
supplying ammonia (NH3) and tri-methyl-aluminum (TMA) at 1175° C. for growing the AlN layer, then, cooling down a temperature of a substrate to 1000° C. under atmosphere of nitrogen (N2) mixed with ammonia (NH3), and finally growing a GaN layer with a thickness of 480 nm by supplying ammonia (NH3) and tri-methyl-gallium (TMG)
Data Source
AI summary
A process of forming an epitaxial wafer is disclosed. The process includes steps of (a) growing an aluminum nitride (AlN) layer at a first temperature and a first flow rate of ammonia (NH3); and (b) growing a gallium nitride (GaN) layer on the AlN layer. The step (b) includes a first period and a second period. At least one of a temperature from the first temperature to a second temperature that is lower than the first temperature and a flow rate of NH3 from the first flow rate to a second flow rate different from the first flow rate is carried out during the first period. The second period grows the GaN layer at the second temperature and the second flow rate of NH3.