Wafer Surface Oxidation Method for Thickness Uniformity
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Solution Overview
Problem
The existing thermal oxidation methods for silicon wafers in vertical furnaces result in non-uniform oxidation layer thickness due to temperature gradients, leading to asymmetrical growth across the wafer surface.
Innovation Solution
A surface oxidation method involving a temperature raising step followed by an isothermal oxidation step in an annealing furnace with a vertical furnace tube and a gas intake conduit, where the temperature is raised from 400° C. to 1100° C. at a rate greater than 5° C./min, forming a first oxidation layer thicker at the center and a second layer thicker at the center during isothermal conditions, achieving radial thickness uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If gas is injected from a gas conduit parallel to the wall of the furnace at low temperature, then the gas can flow from bottom to top and reach the shower-head-shaped conduit, but the temperature of the side furnace wall is lowered, resulting in non-uniform temperature distribution and non-uniform oxidation layer thickness
Solution Approach 1:
The patent applies preliminary action by performing a temperature raising step before the isothermal oxidation step. During this preliminary phase, the furnace temperature is rapidly increased while the wafer is rotated, allowing the oxidation layer to grow with a thickness distribution that is thicker at the center and thinner at the edges. This preliminary thickness distribution is designed to compensate for the temperature gradient that will exist during the subsequent isothermal oxidation phase, ultimately achieving uniform overall thickness.
Solution Approach 2:
The patent applies parameter changes by transitioning from a dynamic temperature condition (temperature raising at >5°C/min) to a static isothermal condition. This parameter change allows the oxidation process to proceed in two distinct phases: first under conditions that create a specific thickness gradient, then under stable conditions that add a complementary gradient, resulting in uniform final thickness despite the presence of furnace temperature gradients.
2Manufacturing precision
If the temperature is raised rapidly at a rate greater than 5° C./min during oxidation atmosphere, then the first oxidation layer can be formed with compensatory thickness distribution, but the process time is extended compared to conventional methods
Solution Approach 1:
The patent applies segmentation by dividing the oxidation process into two distinct sequential steps: a temperature raising step and an isothermal oxidation step. This segmentation allows each step to serve a specific function - the first step creates a thickness distribution pattern, while the second step completes the oxidation under stable conditions. The sum of these two time periods achieves uniform thickness while managing the trade-off with process time.
3Manufacturing precision
If the wafer is panned during temperature raising and isothermal oxidation, then the oxidation layer thickness can be symmetrically compensated to achieve radial uniformity, but the device complexity increases due to the need for precise rotation control
Solution Approach 1:
The patent applies dynamics by introducing rotation of the wafer during the oxidation process. Instead of keeping the wafer stationary, it is rotated to ensure uniform exposure to the oxidation atmosphere and to facilitate the formation of a symmetrically compensated thickness distribution. This dynamic element helps achieve radial uniformity despite temperature gradients, though it does increase operational complexity.
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 compensates for thickness asymmetry, resulting in a uniformly thick oxidation layer across the wafer, enhancing the radial uniformity of the oxidation process.
Implementation Method 1
raising the temperature to an oxidation temperature (in the range of from 800° C. to 1100° C.), starting injecting oxygen or a mixture of oxygen and hydrogen, which is a primary oxidation stage
Data Source
AI summary
A surface oxidation method for a wafer, the method comprises: raising a temperature on the wafer in an oxidation atmosphere, the temperature is raised from a start temperature to a target temperature at a temperature raising rate greater than 5° C./min, the temperature is raised in a vertical furnace tube of an annealing furnace, the vertical furnace tube includes a gas intake conduit arranged on a side wall, the gas intake conduit includes a gas inlet arranged to be proximate to a bottom of the vertical furnace tube and a gas outlet arranged to be proximate to a top of the furnace tube, the wafer overlying the vertical furnace tube; and isothermally oxidizing the wafer at the target temperature in the oxidation atmosphere.