Nitride Semiconductor Substrate Epitaxy for Low-Dislocation Surfaces
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Solution Overview
Problem
The ELO method for growing nitride semiconductor substrates faces challenges in reducing dislocation density when the pitch of the mask layer is lengthened, leading to difficulties in forming a facet structure with a sharp top and increasing the time required to flatten the crystal layer, which reduces productivity.
Innovation Solution
A method involving a vapor deposition process where a base substrate with a (0001) plane is used, with a mask layer having openings, and by growing a first layer with inclined interfaces that expand and contract, allowing the (0001) plane to disappear, followed by a second layer with a mirror surface, resulting in a substrate with low dislocation density regions and high dislocation density regions arranged alternately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the pitch of the mask layer is lengthened to widen the low dislocation density region, then the area of low dislocation density region is improved, but the facet structure cannot form with a sharp top and the (0001) plane disappears incompletely, causing dislocations to propagate to the surface
Solution Approach 1:
The patent applies preliminary action by forming a buffer layer with specific thickness before growing the crystal layer. This buffer layer is prepared in advance to ensure proper facet structure formation and dislocation bending, preventing dislocations from reaching the surface while maintaining a wide low dislocation density region.
Solution Approach 2:
The patent changes parameters by optimizing the thickness of the buffer layer and the pitch of the mask layer within specific ranges. By adjusting these parameters, the method achieves both a wide area of low dislocation density and complete disappearance of the (0001) plane, resolving the contradiction between area expansion and manufacturing precision.
2Productivity
If the pitch of the mask layer is lengthened to increase opening width, then the productivity is improved by reducing the number of masks, but the height from the main surface to the top of the facet structure is increased, requiring longer flattening time
Solution Approach 1:
The patent optimizes the pitch of the mask layer and the thickness of the buffer layer within specific parameter ranges. This parameter optimization allows for longer pitch (improving productivity) while maintaining appropriate facet structure height, thus reducing flattening time and resolving the contradiction between productivity and time loss.
3Device complexity
If the pitch of the mask layer is lengthened to reduce the number of masks, then the device complexity is reduced, but it becomes difficult to make the (0001) plane disappear during growth, reducing manufacturing precision
Solution Approach 1:
The patent changes the parameters of buffer layer thickness and mask layer pitch to specific ranges that enable the (0001) plane to disappear completely during crystal growth. This parameter optimization allows for simplified mask structures with longer pitch while maintaining high manufacturing precision for facet structure formation.
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 efficiently lowers dislocation density on the nitride semiconductor substrate surface, improving productivity by allowing for quicker mirror finishing of the second layer and reducing the inclusion of high dislocation density regions in semiconductor devices.
Implementation Method 1
a first step of epitaxially growing a single crystal of a group III nitride semiconductor on the main surface of the base substrate through the openings of the mask layer
Implementation Method 2
gradually expanding the inclined interfaces toward an upper side of the main surface of the base substrate, making the (0001) plane disappear from the top surface
Implementation Method 3
a second step of epitaxially growing a single crystal of a group III nitride semiconductor on the first layer, making the inclined interfaces disappear, and growing a second layer having a mirror surface
Data Source
AI summary
A method for manufacturing a nitride semiconductor substrate, including: a step of preparing a base substrate; a step of forming a mask layer having a plurality of openings on the main surface of the base substrate; a first step of growing a first layer whose surface is composed only of inclined interfaces; and a second step of epitaxially growing a single crystal of a group III nitride semiconductor on the first layer, making the inclined interfaces disappear, and growing a second layer having a mirror surface, wherein in the first step, at least one valley and a plurality of tops are formed at an upper side of each of the plurality of openings of the mask layer by forming a plurality of concaves on a top surface of the single crystal and making the (0001) plane disappear.