Silicon Wafer Cracking Resistance via Surface Treatment
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Solution Overview
Problem
Silicon wafers experience cracking due to extremely high stress generated during rapid heating and cooling processes like FLA and LSA, which restricts treatment conditions in device manufacturing, necessitating a solution to enhance cracking resistance.
Innovation Solution
A method of manufacturing silicon wafers that involves setting stress and inspecting defects on the surface to ensure the stress times defect size satisfies a specific criterion (Stress S×Size of defect C≦3500 MPa·μm), limiting the number of large defects on the back surface, and optimizing oxygen concentration to prevent cracking during high-temperature, short-time heat treatments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If rapid heating and cooling process (FLA/LSA) is used to achieve higher degree of integration and shorter processing time, then productivity is improved, but the wafer experiences extremely high stress causing cracking
Solution Approach 1:
The patent applies preliminary action by performing surface treatment on the wafer before the FLA/LSA heat treatment process. This pre-treatment modifies the surface properties to enhance stress resistance, preventing cracking during the subsequent rapid heating and cooling process. The surface treatment is conducted in advance to prepare the wafer for the harsh thermal conditions it will encounter during productivity-enhancing processing.
2Reliability
If high temperature heat treatment (1100°C to melting point) is applied for short time (1μ second to 100 m seconds) to activate impurities, then electrical activation is improved, but thermal stress causes wafer cracking
Solution Approach 1:
The patent applies parameter changes by modifying the surface properties of the wafer through surface treatment, which changes the mechanical and thermal parameters of the surface layer. This modification allows the wafer to withstand the extreme temperature conditions (1100°C to melting point) and associated thermal stress while maintaining the necessary electrical activation properties during the short-duration heat treatment process.
3Reliability
If conventional RTA method is used to prevent cracking through oxygen precipitate, then wafer integrity is maintained, but processing time is too long and temperature conditions are too harsh for advanced nodes
Solution Approach 1:
The patent applies the taking out principle by removing the dependency on oxygen precipitates for crack prevention. Instead of relying on the conventional RTA mechanism where oxygen precipitates stop slippage extension, the invention uses surface treatment to directly enhance stress resistance, extracting the crack prevention function from the bulk oxygen precipitate mechanism and implementing it through surface modification alone.
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
The method effectively prevents cracking in silicon wafers during harsh heat treatments, maintaining electrical activation of impurities and achieving a rectangular impurity profile, even under conditions that typically lead to cracking.
Implementation Method 1
a wafer is heated to an initial temperature of 400° C. to 600° C., and only a surface of the wafer is rapidly heated to a temperature from 1100° C. to a silicon melting point by irradiating an entire surface of the wafer with a short wavelength light, for example, from a Xe lamp
Implementation Method 2
The surface of the wafer is rapidly heated to a temperature from 1100° C. to a silicon melting point
Implementation Method 3
and then rapidly cooled. A heat treatment time is in units (on the order) of μ second to m second
Implementation Method 4
a temperature difference of several hundred ° C. is generated between the front and back surfaces of a wafer
Implementation Method 5
Therefore, an extremely high stress is applied to the wafer compared to the case that the conventional RTA (Rapid Thermal Annealing) is performed
Data Source
AI summary
This method of manufacturing a silicon wafer has a step of preparing a wafer, in which a surface of the silicon wafer is surface-treated, a step of setting stress, in which the stress S (MPa) subjected on the wafer is set, a step of inspecting, in which a defect on a surface of the wafer is inspected, and a step of determining, in which the wafer is evaluated if the wafer satisfies a criterion. In this method, it is possible to manufacture a wafer with cracking resistance even if it is subjected to a millisecond annealing by the FLA annealing treatment.