Monocrystalline Silicon Pulling with Variable Diameter for Resistivity Control
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Solution Overview
Problem
Existing methods for manufacturing monocrystalline silicon using the Czochralski method face challenges in achieving high yield rates while maintaining low resistivity and high dopant concentration, often resulting in abnormal crystal growth and decreased product yield.
Innovation Solution
The method involves pulling up monocrystalline silicon from a dopant-added melt using the Czochralski process, with a specific structure comprising a shoulder, a straight body, and a tail. The straight body is divided into a first straight body with a first diameter and a second straight body with a second diameter larger than the first, allowing for controlled resistivity and dopant concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a large amount of dopant is charged in the silicon melt to achieve high dopant concentration and low resistivity, then the freezing-point depression becomes extremely large causing constitutional undercooling, but this leads to abnormal crystal growth and decreased manufacturing reliability
Solution Approach 1:
The patent applies preliminary action by forming a shoulder portion with a larger diameter before forming the straight body portion. This shoulder portion pre-accommodates the dopant concentration gradient and constitutional undercooling effects, allowing the subsequent straight body to grow with stable monocrystalline structure and controlled resistivity without abnormal crystal growth
Solution Approach 2:
The patent applies local quality by creating different structural zones along the crystal growth direction - the shoulder portion with larger diameter serves a different function (accommodating dopant gradient) than the straight body portion (providing uniform low resistivity). This local differentiation allows high dopant concentration in specific regions without causing overall crystal instability
2Ease of manufacture
If the straight body diameter is kept uniform to simplify manufacturing, then the process is easier to control, but the acquisition ratio of wafers with target resistivity decreases due to dopant accumulation at the solid-liquid interface
Solution Approach 1:
The patent applies segmentation by dividing the straight body into multiple zones with different diameters - a first straight body portion with smaller diameter and a second straight body portion with larger diameter. This segmentation allows different sections to serve different functions: the first portion provides uniform diameters for easy manufacturing control, while the second portion with larger diameter accommodates dopant accumulation to maintain target resistivity and increase wafer acquisition ratio
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 enables the high-yield production of monocrystalline silicon with extremely low resistivity, improving the acquisition ratio of wafers with target resistivity and extending the length of the straight body while maintaining low resistivity.
Implementation Method 1
a freezing-point depression, which is a difference between a freezing point of a silicon melt and a freezing point of a dopant-added melt that is the silicon melt added with a dopant, becomes extremely large by charging a large amount of the dopant in the silicon melt
Implementation Method 2
the dopant that has not been accommodated in the monocrystalline silicon is discharged into the dopant-added melt to accumulate near the solid-liquid interface, so that the dopant concentration comes into such a concentration distribution that the dopant concentration decreases exponentially from a concentration at the solid-liquid interface according to a distance from the solid-liquid interface
Data Source
AI summary
A monocrystalline silicon includes a shoulder, a straight body, and a tail. The straight body includes: a first straight body having a first diameter d1; and a second straight body provided closer to the shoulder than the first straight body is and having a second diameter d2 larger than the first diameter d1 by from 3.5% to 15%. Firstly, a resistivity at a start point of the straight body connected to the shoulder is set to a first resistivity. Subsequently, the monocrystalline silicon is pulled up and grown to form the first straight body, and a resistivity at a start point of the first straight body is set to a second resistivity lower than the first resistivity.