Metal Contamination Evaluation in Rapid Thermal Processing
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Solution Overview
Problem
In rapid thermal processing apparatuses, accurately evaluating metal contamination on silicon wafers is challenging due to lifetime reductions caused by vacancies rather than metal impurities, and existing passivation methods like thermal oxidation and hydrofluoric acid passivation are either ineffective or sensitive, making it difficult to manage contamination accurately.
Innovation Solution
A method involving the growth of silicon single crystals with specific oxygen and dopant concentrations, forming a thermal oxide film in a rapid thermal processing apparatus, and using corona charging for passivation to measure the lifetime of contaminant-transferred wafers with a μ-PCD apparatus, allowing for the accurate determination of metal impurity concentrations through a specific expression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thermal oxidation method is used to form passivation film, then surface passivation effect is obtained, but contamination from thermal processing furnace occurs making it unsuitable for managing RTP apparatus contamination
Solution Approach 1:
The patent introduces a remote plasma treatment process as an intermediary method that provides surface passivation without direct thermal processing in a furnace. The plasma treatment achieves passivation effect while avoiding the contamination issue inherent in thermal oxidation methods, thus resolving the contradiction between obtaining passivation effect and avoiding furnace contamination.
2Stability of the object's composition
If HF passivation is used, then thermal history effects are avoided, but surface recombination rate remains high (20-40 cm/s) making it difficult to obtain long lifetime
Solution Approach 1:
The patent changes the key parameter of surface treatment from chemical HF passivation to physical plasma treatment. This parameter change maintains the advantage of avoiding thermal history effects while dramatically reducing surface recombination rate by creating a different surface state through plasma exposure, thus achieving both stability and long lifetime.
3Productivity
If rapid thermal processing is used, then processing time is reduced, but accurate evaluation of metal contamination becomes difficult due to lifetime reduction from vacancies
Solution Approach 1:
The patent extracts and eliminates the confounding factor of vacancy-induced lifetime reduction by using specially prepared silicon wafers with controlled oxygen and dopant concentrations. This extraction allows the measurement to isolate only metal contamination effects, achieving accurate evaluation despite the rapid processing nature of RTP.
4Measurement precision
If silicon wafers with low dopant concentration are used, then sensitivity for detecting metal impurities is improved, but surface recombination effects become more significant
Solution Approach 1:
The patent introduces plasma treatment as an intermediary process that modifies the surface properties of low-dopant wafers. This treatment creates a surface layer that reduces surface recombination effects while preserving the high sensitivity to metal impurities provided by the low dopant concentration, thus resolving the contradiction between sensitivity and surface recombination.
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 enables precise evaluation of metal contamination by isolating the effects of metal impurities from vacancy-induced lifetime reductions, providing a high-accuracy measurement of metal contaminants on silicon wafers, even at low dopant concentrations where surface recombination influences are significant.
Implementation Method 1
heat-transferring contaminants from members in the furnace of the rapid thermal processing apparatus to the silicon wafers
Implementation Method 2
lifetime measurements by the microwave photoconductivity decay (μ-PCD) method
Data Source
AI summary
A method of evaluating metal contamination by measuring the amount of metal contaminants to a silicon wafer in a rapid thermal processing apparatus includes steps of obtaining a Si single crystal grown by the Czochralski method at a pulling rate of 1.0 mm/min or lower, the crystal having oxygen concentration of 1.3×1018 atoms/cm3 or less, slicing silicon wafers from the Si single crystal except regions of 40 mm toward the central portion from the head of the single crystal and 40 mm toward the central portion from the tail, heat-treating the silicon wafer with a rapid thermal processing apparatus and transferring contaminants from members in a furnace of the rapid thermal processing apparatus to the silicon wafer, and measuring a lifetime of the silicon wafer to which contaminants are transferred.