Silicon Wafer Doping Uniformity in Diffusion Ovens
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Solution Overview
Problem
Achieving uniform doping profiles across multiple silicon wafers simultaneously in a diffusion oven is challenging, particularly in horizontal furnaces with long chambers and densely packed wafers, due to gas depletion and varying reaction conditions.
Innovation Solution
The method involves modifying the flow rates of reaction, doping, and carrier gases during the doping process, using variable throughput valves controlled by a programmable controller, to optimize gas distribution and achieve homogeneous wetting across the wafer set, with specific ratios and flow rates adjusted based on the position within the oven.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a horizontal furnace with long chamber is used to process large number of wafers simultaneously, then productivity is improved, but doping uniformity deteriorates due to gas depletion and varying reaction conditions along the chamber length
Solution Approach 1:
The diffusion oven chamber is divided into multiple heating zones with independent temperature control. Each zone can be optimized to compensate for gas depletion effects at different positions, allowing uniform doping across all wafers even when processing large numbers simultaneously in a long horizontal furnace
Solution Approach 2:
Temperature is used as a compensating parameter to offset gas depletion effects. By adjusting temperature distribution along the chamber length (higher temperature in downstream zones where gas depletion occurs), the reaction kinetics are enhanced to maintain uniform doping profiles across all wafer positions
2Manufacturing precision
If gas flow rate is increased to improve wetting homogeneity, then doping uniformity is improved, but process time increases and productivity decreases
Solution Approach 1:
Temperature distribution is optimized to compensate for insufficient gas flow. By increasing temperature in downstream zones, reaction kinetics are enhanced, allowing adequate doping uniformity to be achieved without requiring proportionally high gas flow rates that would extend process time
3Manufacturing precision
If zone control is implemented to compensate for gas depletion, then doping uniformity is improved, but device complexity increases
Solution Approach 1:
The heating system is segmented into multiple independently controllable zones along the chamber length. This segmentation enables localized temperature adjustment to compensate for gas depletion effects at different positions, achieving uniform doping without requiring complex overall system redesign
Solution Approach 2:
Temperature profiles are optimized for each zone based on its position in the chamber. Downstream zones operate at higher temperatures to compensate for gas depletion, while upstream zones operate at lower temperatures. This parameter optimization achieves uniform doping with relatively simple proportional 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 ensures more uniform doping results across the entire set of wafers, allowing for simultaneous processing of a large number of wafers, even in long ovens, by optimizing gas distribution and reaction conditions.
Implementation Method 1
the vapor BBr3 reacts with oxygen inside the reaction chamber following the chemical process
Implementation Method 2
The liquid B2O3 condenses on the silicon wafers
Implementation Method 3
elemental boron diffuses into the silicon wafers as well as into the borosilicate glass (BSG) layer grown in-situ on the silicon surface
Implementation Method 4
The role of the carrier gas is to drive doping agent and reactive gas to the surface of the silicon wafers
Data Source
Figure 1
Figure 2a~3c
Figure 4a~5c
AI summary
The invention provides a method for doping of silicon wafers (8) using a diffusion oven (1), said diffusion oven (1) having a door (2) for loading and unloading of the silicon wafers (8), an inner volume (6), gas inlets (4) for a reaction gas, a doping gas and a carrier gas and means for modifying the flow rate of said reaction gas, said doping gas and said carrier gas into the interior volume (6) of the diffusion oven (1), said method comprising the steps of loading silicon wafers (8) into the diffusion oven (1), heating the diffusion oven (1) in accordance with a predetermined temperature profile at least during a deposition time, letting reaction gas, doping gas and carrier gas flow simultaneously into the inner volume (6) and unloading the doped silicon wafers (8) from the diffusion oven (1), wherein during the deposition time in which reaction gas, doping gas and carrier gas flow simultaneously into the interior volume (6) of the diffusion oven (1), the ratio of the flow rate of reaction gas and flow rate of doping gas is changed at least once from a first ratio to a second ratio and/or the flow rate of the carrier gas is changed at least once from a first flow rate to a second flow rate.