Boron Doping Silicon Wafers via Reduced Pressure BCl3 Process
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Solution Overview
Problem
Current silicon wafer doping processes face challenges with boron doping, including toxicity issues, gas consumption, and limitations in processing large wafers due to aggressive compounds and uneven doping, leading to productivity losses and quality issues.
Innovation Solution
A process operating at reduced pressure using boron trichloride as a precursor, with controlled gas mixing and deposition, allowing for homogeneous and reproducible boron doping of large wafers, optimizing gas flow and oxidation to enhance safety and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If atmospheric pressure doping is used, then the process is simple to operate, but gas consumption increases significantly and uniformity of doping deteriorates
Solution Approach 1:
The patent changes the pressure parameter from atmospheric pressure to reduced pressure (1-30 kPa), which fundamentally alters the gas flow dynamics in the reactor. This parameter change reduces gas consumption while maintaining homogeneous doping uniformity across the wafer surface, as the reduced pressure enables better control of gas distribution without requiring high flow rates.
2Manufacturing precision
If high flow rate gases are used to compensate for enclosure depletion, then doping uniformity improves, but gas consumption and effluent treatment costs increase
Solution Approach 1:
By changing the pressure parameter to reduced pressure (1-30 kPa), the patent achieves efficient gas distribution without requiring high flow rates. The reduced pressure creates optimal conditions for gas penetration and homogeneous deposition, maintaining doping uniformity while significantly reducing gas consumption compared to atmospheric pressure processes.
3Object-affected harmful factors
If boron trichloride is used as precursor, then toxicity is reduced compared to other boron sources, but control of reactivity becomes difficult
Solution Approach 1:
The patent applies parameter changes by operating at reduced pressure (1-30 kPa) and controlling temperature (800-1100°C) to manage the reactivity of boron trichloride. These parameter adjustments enable precise control of the chemical reactions, preventing unwanted side reactions while maintaining the safety advantage of using BCl3 over more toxic alternatives like BBr3 or diborane.
Solution Approach 2:
The patent uses an inert nitrogen atmosphere as carrier gas to transport boron trichloride into the reactor. This inert environment prevents premature reactions and provides stable conditions for controlling the reactivity of BCl3, allowing safe handling and deposition while maintaining reduced toxicity compared to other boron precursors.
4Loss of substance
If moderate oven dimensions are used, then gas consumption is controlled, but processing of large wafers becomes limited
Solution Approach 1:
By changing to reduced pressure operation (1-30 kPa), the patent extends the effective processing capability to large wafers (150 mm diameter and above) without proportionally increasing gas consumption. The reduced pressure enables uniform gas distribution across larger surface areas, allowing the processing of bigger wafers while maintaining controlled gas usage through optimized flow rates adapted to the pressure conditions.
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
Enables the processing of large silicon wafers with high-quality, uniform boron doping, reducing maintenance and gas consumption, and improving safety, making it suitable for photovoltaic cell manufacturing with increased productivity.
Implementation Method 1
react the reactive gases in the enclosure with boron trichloride BCl3 diluted in the carrier gas at a pressure between 1 kPa and 30 kPa, and at a temperature between 800°C and 1100°C, to form a layer of boron oxide glass B2O3
Implementation Method 2
carry out the diffusion of atomic boron in silicon under an N2 +O2 atmosphere at a pressure between 1 kPa and 30 kPa
Data Source
Figure 1
AI summary
The invention relates to a method for p-type boron doping of silicon wafers placed on a stand in a furnace chamber, one end of which comprises a wall in which is arranged a means for injecting reactive gases and a gas carrying a boron precursor in the gaseous state, said method including the following steps: a) causing a reaction in the chamber between the reagent gases and boron trichloride BCl3 diluted in the carrier gas with a pressure of 1 kPa to 30 kPa, and a temperature of 800ºC to 1100ºC, so as to form a layer of boron trioxide B2O3, b) diffusing the atomic boron in the silicon in an atmosphere of N2+O2 with a pressure of 1 kPa to 30 kPa. The invention also relates to a furnace for implementing said doping method as well as to the uses thereof for producing large boron-doped silicon wafers, in particular for photovoltaic applications.