SOI Wafer Thinning via Thermal Oxide Feedback Control
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Solution Overview
Problem
Existing methods for manufacturing SOI wafers struggle to achieve high radial film thickness uniformity due to fluctuations in oxidation rates and radial stock removal variance during the thinning process, making it difficult to meet the precise thickness requirements needed for FD-SOI wafers.
Innovation Solution
A method involving heat treatment to form a thermal oxide film, measuring the SOI film thickness, determining a rotational position based on radial film thickness and stock removal distributions, and rotating the wafer during a two-stage thinning process using batch processing and single wafer cleaning techniques to control etching and achieve precise film thickness adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a two-stage thinning process through forming and removing oxide film together with etching is performed, then the SOI film thickness can be controlled with high accuracy, but radial stock removal variance arises that degrades the radial film thickness distribution
Solution Approach 1:
The patent applies preliminary action by forming a thermal oxide film on the SOI layer surface before the thinning process. This oxide film serves as a sacrificial layer that is subsequently removed, allowing for precise control of the underlying SOI film thickness. The preliminary oxidation step enables accurate thickness measurement and compensation for radial variations in the subsequent etching process, thereby maintaining both thickness control accuracy and radial uniformity.
2Manufacturing precision
If highly accurate uniformity of film thickness is required, then the needs for FD-SOI wafer cannot be met due to radial stock removal variance in the thinning step
Solution Approach 1:
The patent implements feedback control by measuring the SOI film thickness after the oxidation step with the thermal oxide film still present, and then using this measured information to adjust and control the subsequent removal of the oxide film and etching parameters. This closed-loop feedback mechanism compensates for radial stock removal variance and ensures that the final SOI film thickness meets the stringent FD-SOI specifications of ±0.5 nm uniformity across the wafer surface.
3Productivity
If batch processing type heat treatment is used for oxidation, then the process can be performed efficiently, but the oxidation rate changes due to atmospheric pressure fluctuation making it difficult to accurately control oxide film thickness
Solution Approach 1:
The patent uses the thermal oxide film as an intermediary element in the thinning process. By forming this oxide film through batch processing oxidation and then selectively removing it, the system decouples the efficiency benefits of batch processing from the precision requirements of thickness control. The oxide film acts as a mediator that can be uniformly formed in batch mode but whose removal can be precisely controlled to achieve accurate SOI film thickness, thus resolving the contradiction between productivity and manufacturing precision.
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 significantly improves the radial film thickness uniformity of SOI wafers, ensuring that all points on the wafer surface have a thickness within ±0.5 nm of the target value, enhancing the yield and reducing process costs.
Implementation Method 1
heat treatment under an oxidizing gas atmosphere to form a thermal oxide film on a surface of the SOI layer
Implementation Method 2
removing the thermal oxide film on the surface of the SOI layer and etching of the SOI layer... by immersing the SOI wafer in a SC1 solution inside a water tank
Data Source
Figure 1~2(d)
Figure 3~4
AI summary
The present invention is a method for manufacturing an SOI wafer having an SOI layer including a thinning step to adjust an SOI film thickness of the SOI wafer, including the steps of: (A1) measuring the SOI film thickness of the SOI wafer having the SOI layer before the thinning step; (A2) determining a rotational position of the SOI wafer in the thinning step on the basis of a radial SOI film thickness distribution obtained in the measuring of the film thickness and a previously determined radial stock removal distribution in the thinning step, and rotating the SOI wafer around the central axis thereof so as to bring the SOI wafer to the determined rotational position; and (A3) thinning the SOI layer of the rotated SOI wafer. This provides a method for manufacturing an SOI wafer which can produce an SOI wafer with an excellent radial film thickness uniformity of the SOI layer after the thinning step.