Silicon Ingot Resistivity Control via Pilot Ingots
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Solution Overview
Problem
The Czochralski method for producing single crystal silicon ingots faces challenges in achieving consistent high resistivity and preventing type changes due to impurity segregation, leading to a significant portion of ingots falling outside product specifications.
Innovation Solution
The method involves adding gallium or indium as a dopant before growing a sample ingot, measuring its resistivity, and adjusting the amount of a second dopant based on the measured resistivity to produce a product ingot with targeted high resistivity and maintaining the ingot type, using a solid-phase alloy to facilitate precise control and compensation for impurity segregation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the Czochralski method is used to grow single crystal silicon ingots, then high-purity silicon can be produced, but impurity segregation causes resistivity variation and type changes along the ingot length
Solution Approach 1:
A pilot ingot is grown first to characterize the melt's impurity content and resistivity before producing the main product ingot. This preliminary action allows determination of the exact dopant amount needed to achieve target resistivity, preventing type changes and ensuring uniformity throughout the product ingot.
Solution Approach 2:
The resistivity of the pilot ingot is measured to provide feedback on the melt's actual composition. This feedback is used to calculate and adjust the precise amount of dopant (boron, phosphorus, or gallium) to be added to the melt before growing the product ingot, ensuring target resistivity is achieved.
2Reliability
If highly pure polysilicon is used for high resistivity ingot production, then the base material quality is improved, but the spread in impurity profile causes wide spread in intrinsic resistivity range
Solution Approach 1:
The method changes the chemical composition parameters of the melt by adding specific dopants (boron, phosphorus, or gallium) in calculated amounts. This adjusts the intrinsic resistivity and compensates for the spread in impurity profile present in highly pure polysilicon, achieving uniform target resistivity in the final ingot.
Solution Approach 2:
The pilot ingot serves as a feedback mechanism to characterize the actual impurity content of the highly pure polysilicon feedstock. This allows precise calculation of dopant addition requirements to compensate for variations in the polysilicon's impurity profile, achieving consistent resistivity control.
3Manufacturing precision
If additional dopant is added to control resistivity and ingot type, then resistivity control is improved, but very small amounts of dopants must be added making the process difficult
Solution Approach 1:
The pilot ingot is grown first to establish baseline resistivity and impurity content before adding dopants to the main melt. This preliminary characterization allows calculation of the precise dopant amount needed, simplifying the subsequent doping process and ensuring accurate resistivity control.
Solution Approach 2:
The method uses calculated parameter changes in dopant concentration based on pilot ingot measurements. By determining the exact amount of dopant needed from the pilot run, the actual doping process becomes more straightforward and controllable, avoiding the difficulty of adding very small amounts without precise guidance.
4Manufacturing precision
If dopants are added to maintain high resistivity, then the ingot type can be controlled, but the separation of dopant addition from crystal growth complicates the process
Solution Approach 1:
The dopant is added to the melt before the crystal growth process begins, using the pilot ingot to determine the exact amount needed. This preliminary dopant addition integrated with the melt preparation simplifies the overall process compared to attempting to control type during growth, while maintaining precise ingot type control.
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 reduces resistivity variation, increases the prime portion of the ingot, and simplifies doping processes, improving resistivity control and reducing errors in resistivity measurements, while maintaining the ingot type and achieving high resistivity targets.
Implementation Method 1
impurities in the melt may segregate due to a segregation coefficient which causes the impurity to concentrate in the melt which causes the amount incorporated into the ingot to increase as the ingot is grown
Implementation Method 2
require wafers with a relatively high resistivity such as 1500 ohm-cm (Ω-cm) or more
Implementation Method 3
The polycrystalline silicon is heated to cause a silicon melt to form in the crucible
Implementation Method 4
Single crystal silicon, which is the starting material for most processes for the fabrication of semiconductor electronic components, is commonly prepared by the so-called Czochralski (CZ) process wherein a single seed crystal is immersed into molten silicon and then grown by slow extraction
Data Source
AI summary
Methods for forming single crystal silicon ingots with improved resistivity control and, in particular, methods that involve gallium or indium doping are disclosed. In some embodiments, the ingots are characterized by a relatively high resistivity.