Silicon Wafer Metal Contamination Evaluation via Corona Charging
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Solution Overview
Problem
Existing methods for evaluating metal contamination on silicon wafers, particularly those with an RTO film formed by heat treatment, face challenges in detecting contamination by metals that do not affect the lifetime as a single atom and in accurately measuring lifetime due to noise from crystal defects.
Innovation Solution
The method involves adjusting the condition of the RTO film through specific heat treatment processes before corona charging, allowing for more accurate lifetime measurement by the μ-PCD method. This includes holding the silicon wafer at temperatures between 1250°C and 1330°C for 7 to 220 seconds under an oxygen atmosphere, and then lowering the temperature at rates between 30°C/s and 500°C/s, or holding it at temperatures between 1020°C and 1250°C for 7 to 600 seconds with temperature lowering rates between 1°C/s and 280°C/s.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lifetime measurement is performed on silicon wafer with RTO film formed by heat treatment, then metal contamination detection is enabled, but measurement precision deteriorates due to recombination centers at the interface
Solution Approach 1:
Corona charging is performed as a preliminary treatment before lifetime measurement to deposit ions on the oxide film surface. This preliminary action creates an electric field that repels minority carriers from the interface region, preventing their annihilation at recombination centers and enabling accurate bulk lifetime measurement
Solution Approach 2:
The corona-charged oxide film acts as an intermediary layer that mediates between the silicon bulk and the measurement system. The deposited ions on the oxide film create a potential barrier that selectively blocks carrier flow to interface recombination centers while allowing the measurement of bulk carrier lifetime
2Manufacturing precision
If heat treatment is performed at high temperature to form RTO film, then oxide film formation is achieved, but crystal defects increase causing measurement noise
Solution Approach 1:
The patent optimizes heat treatment parameters (temperature, time, atmosphere) to form oxide films with controlled thickness and quality. By carefully controlling these parameters, the oxide film serves as an effective corona charging substrate without introducing excessive crystal defects that would degrade measurement quality
3Ease of operation
If conventional lifetime measurement method is used on silicon wafer with RTO film, then measurement process is simple, but detection sensitivity deteriorates for metals not affecting lifetime as single atom
Solution Approach 1:
The patent combines corona charging with μ-PCD lifetime measurement in a continuous process. The corona charging pretreatment is followed immediately by lifetime measurement, creating a continuous evaluation process that maintains high detection sensitivity while preserving operational simplicity through automation
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 enables highly accurate evaluation of metal contamination on silicon wafers by improving the sensitivity of lifetime measurements and reducing noise from crystal defects, thus facilitating better management of metal contamination in semiconductor manufacturing.
Implementation Method 1
heat treatment may be applied to the silicon wafer mainly for the recovery of ion implantation damage
Implementation Method 2
an oxide film formed on a silicon wafer surface by heat treatment under an oxygen atmosphere in the RTP apparatus
Implementation Method 3
ions generated by corona discharge are deposited on the oxide film (RTO film) and the carriers near the interface are confined to the bulk
Implementation Method 4
excess carriers (electron-hole pairs) are generated by pulsed irradiation of a silicon wafer with an excited laser beam
Implementation Method 5
The time for the resistivity to return to the initial state by recombination of the excess carriers is measured from the microwave reflectivity
Data Source
AI summary
A method of accurately evaluating the metal contamination on silicon wafers by lifetime measurement. The silicon wafers are subjected to heat treatment and further to a corona charge as passivation, and then, the lifetime is measured, in which the heat treatment is at least one of the following processes that the silicon wafer is held at a temperature of 1250° C. or more to 1330° C. or less for 7 s or more to 220 s or less under an oxygen atmosphere and then the temperature is lowered at a rate of 30° C./s or more to 500° C./s or less, or that and the silicon wafer is held at a temperature of 1020° C. or more to less than 1250° C. for 7 s or more to 600 s or less under an oxygen atmosphere, and then the temperature is lowered at a rate of 1° C./s or more to 280° C./s or less.