Semiconductor Thin Film Crystallization via Inverted Thermal Gradient
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Solution Overview
Problem
Existing methods for producing semiconductor thin films on foreign substrates are limited in achieving large single crystal sizes, as the different crystal structure of the substrate interferes with the growth of semiconductor single crystals, resulting in average sizes not exceeding several mm in diameter and 50 μm in thickness.
Innovation Solution
A method involving the application of a thin layer of polycrystalline semiconductor material on a foreign substrate, heating it above the melting point, and then slowly cooling it while maintaining a temperature gradient that decreases from the substrate contact surface to the film surface, allowing the film to crystallize from the surface downwards, promoting the growth of extensive single crystals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional PVD, CVD, or PECVD methods are used to apply polycrystalline semiconductor material followed by zone melting or annealing, then a thin film with semiconductor single crystals is produced, but the average single crystal size is limited to not exceeding several mm in diameter and 50 μm in thickness
Solution Approach 1:
The invention changes the temperature parameter profile during crystallization, specifically maintaining a temperature gradient where the substrate temperature is higher than the film temperature. This parameter change enables the film to crystallize from the substrate interface upward, promoting growth of extensive single crystals with diameters exceeding several mm and thicknesses greater than 50 μm, thereby resolving the limitation on single crystal size while using conventional deposition methods
Solution Approach 2:
The invention inverts the conventional crystallization approach by heating the substrate to a temperature higher than the melting point of the semiconductor material, causing the film to crystallize from the substrate interface upward rather than from the surface downward or simultaneously from both interfaces. This inverted crystallization direction allows single crystals to grow extensively without being constrained by the substrate's crystal structure, achieving larger single crystal sizes
2Manufacturing precision
If the foreign substrate is heated above the melting temperature of the semiconductor thin film and then slowly cooled, then single crystals can grow in thickness, but the different crystal structure of the substrate interferes with the formation of large semiconductor single crystals
Solution Approach 1:
The invention changes the temperature parameter relationship between substrate and film, maintaining substrate temperature higher than film temperature during the critical crystallization phase. This parameter change creates a thermal gradient that drives crystallization from the substrate interface upward, allowing single crystals to grow extensively in thickness while minimizing the interfering effect of the substrate's different crystal structure
Solution Approach 2:
The temperature gradient acts as an intermediary mechanism that mediates between the substrate's crystal structure and the semiconductor film's crystallization. By maintaining a controlled temperature difference, the invention enables the film to crystallize in a direction (from substrate upward) that reduces the adverse influence of the substrate's different crystal structure, allowing extensive single crystal growth
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 increases the average single crystal size by one order of magnitude, achieving larger semiconductor single crystals with improved film quality, particularly in thin film solar cells.
Implementation Method 1
the foreign substrate is heated to such an extent that the semiconductor thin film melts at a temperature which is higher than the melting temperature of the semiconductor thin film
Implementation Method 2
the temperature is slowly decreased to below the melting temperature of the semiconductor thin film and to solidification of the semiconductor thin film
Data Source
AI summary
The invention relates to a method by means of which the average single crystal size, in particular the diameter of the single crystals, in a semiconductor thin film applied to a foreign substrate can be increased by an order of magnitude with respect to prior methods. The method is characterized in that a thin semiconductor film is applied to the foreign substrate in a first step. Then the foreign substrate is heated to such an extent that the semiconductor thin film melts. Then the temperature is slowly decreased to below the melting temperature of the semiconductor material. During the cooling process, the foreign substrate is heated in such a way that, proceeding from the surface of the foreign substrate, the temperature continuously decreases in a vertical direction perpendicular through the semiconductor thin film to the surface of the thin film. It is thereby ensured that the thin film crystallizes, or rather solidifies, in the opposite direction during the slow decrease of the temperature to below the melting temperature of the semiconductor thin film. In other words, the atom layers directly at the exposed surface of the thin film crystallize first, then the next deeper atom layers crystallize, etc., until finally the atom layers in the immediate vicinity of the surface of the foreign substrate crystallize. The atom layers directly at the exposed surface of the thin film can freely orient themselves without interference during the crystallization, whereby the formation of extensive single crystals several atom layers thick is promoted. Said extensive single crystals are then used as growth nuclei for the next deeper atom layers in such a way that said extensive single crystals grow in thickness in the direction of the surface of the foreign substrate. Only the atom layers in the immediate vicinity of the surface of the foreign substrate are interfered with during the crystallization and degrade into an amorphous or polycrystalline boundary layer. In order to ensure the aforementioned temperature course perpendicular through the thin film, either a heat source applied to the underside of the foreign substrate in a planar manner or heating of the foreign substrate by means of electric current passage must be selected as the heating type. The method is suitable in particular for producing highly efficient thin film solar cells. The method is also suitable for high-quality annealing of high-temperature semiconductor thin films.