Crystalline Semiconductor Stack for Grain-Boundary-Free TFT Channels
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Solution Overview
Problem
Solid phase crystallization and solid phase epitaxy methods for forming Si, SiGe, and Ge films in semiconductor devices often result in grain boundaries at undesired locations, limiting device performance and reliability, especially in applications like vertical thin-film transistors.
Innovation Solution
A semiconductor structure is formed by layering a first material with a blocking material of higher crystallization temperature between a second and third material, where the second material has a higher crystallization temperature than both, and the structure is annealed above the crystallization temperature of the third material but below that of the second, preventing grain boundary formation within the second material by 'seeding' crystallization from the third material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solid phase crystallization or solid phase epitaxy is used to form Si, SiGe, and Ge films, then crystalline structures can be formed, but grain boundaries occur at unwanted locations which limit device performance and reliability
Solution Approach 1:
A blocking material layer is deposited beforehand between the second and third materials to prevent grain boundary formation. This preliminary structural preparation ensures that when crystallization occurs, grain boundaries are blocked from forming at critical interfaces, thereby improving device reliability while maintaining manufacturing feasibility
Solution Approach 2:
The blocking material acts as an intermediary layer between the second and third materials with different crystallization temperatures. This intermediate layer prevents direct interaction that would otherwise create grain boundaries, serving as a mediator that controls the crystallization process and eliminates harmful grain boundary formations
2Temperature
If a lower-Tc material is placed above and below a higher-Tc material to enable lower temperature crystallization, then crystallization can be performed at relatively lower temperature, but grain boundaries form within the higher-Tc material as it crystallizes from both sides
Solution Approach 1:
The harmful effect of grain boundary formation is extracted and removed by introducing a blocking material layer. This layer takes out the problem of grain boundary formation that occurs when lower-Tc materials are placed above and below higher-Tc materials, allowing the temperature advantage to be maintained while eliminating the precision problem
Solution Approach 2:
The blocking material serves as an intermediary that prevents the higher-Tc material from crystallizing from both sides simultaneously. By blocking the crystallization front propagation, it prevents grain boundary formation while allowing the system to operate at lower temperatures enabled by the lower-Tc materials
3Ease of manufacture
If grain boundaries are present in the crystalline structure, then material can be formed using conventional methods, but device performance and reliability are limited
Solution Approach 1:
The blocking material acts as an intermediary layer that prevents grain boundary formation without complicating the manufacturing process. It is deposited as an additional layer between existing materials, maintaining process simplicity while dramatically improving device reliability by eliminating grain boundaries
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 method allows for the formation of continuous crystalline structures without grain boundaries, enhancing the uniformity and reliability of semiconductor devices, particularly suitable for vertical thin-film transistors, and enabling thicker crystalline material formation without damage to electronic components.
Implementation Method 1
the structure is annealed above the crystallization temperature of the third material but below that of the second, preventing grain boundary formation within the second material by 'seeding' crystallization from the third material
Implementation Method 2
Solid phase crystallization (SPC) and solid phase epitaxy (SPE) are conventionally used to form Si, SiGe, and Ge films for solid state electronics
Implementation Method 3
a film stack is formed having sections of material having varying crystallization temperatures. As the stack is heated above the Tc of one section, crystallization begins. The material with a lower Tc can 'seed' crystallization of the material with the higher Tc
Data Source
AI summary
A device comprises a first crystalline material, a second material in a substantially crystalline form, a blocking material between the first crystalline material and the second material, and a third material in a substantially crystalline form and adjacent the second material. A crystallization temperature of the third material is different from a crystallization temperature of the second material. At least one of the second material and the third material is substantially free of a grain boundary therein. Also disclosed is a device including a transistor. The transistor comprises a first crystalline material, a substantially continuous crystalline structure, and a blocking material between the first crystalline material and the substantially continuous crystalline structure. The substantially continuous crystalline structure comprises a second crystalline material and a third crystalline material having a different crystallization temperature than the second crystalline material. The substantially continuous crystalline structure is substantially free of a grain boundary therein.