Silicon Wafer Laser Gettering for Dislocation Control

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Solution Overview

Problem

Existing methods for forming gettering sites in silicon wafers, such as the IG and PBS methods, are inefficient and prone to internal stress-induced dislocation, especially in large-diameter wafers, which deteriorates device characteristics.

Innovation Solution

Irradiating a silicon wafer with a first laser beam of relatively long wavelength and a second laser beam of relatively short wavelength at predetermined depths to form a process-affected layer for gettering heavy metals, while the second laser beam melts and recrystallizes the surface layer to suppress dislocation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a low-output laser beam is used to form a gettering site by multiphoton absorption, then the formation time is short, but internal stress-induced dislocation occurs due to thermal impulse

Engineering Contradiction:

Improvegettering site formation timeVSAvoiddevice characteristics

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent changes the laser beam parameters by using a high-output laser beam instead of a low-output laser beam. This parameter change allows the formation of a gettering site without generating excessive thermal impulse that causes dislocation, while still maintaining short formation time through the multiphoton absorption process

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies beforehand cushioning by performing a thermal process (heating and cooling) after laser irradiation to relieve internal stresses before they can cause dislocation. This pre-cushioning approach prevents the deterioration of device characteristics while maintaining the benefits of short formation time

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

2Reliability

If a long-time heat treatment is used to form an oxygen precipitate portion, then the gettering site is formed, but the production cost increases and heavy metal contamination may occur

Engineering Contradiction:

Improvegettering site formationVSAvoidheat treatment time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent replaces the thermal field (heat treatment) with an optical field (laser beam irradiation). The laser beam induces multiphoton absorption to form the gettering site directly, eliminating the need for long-time heat treatment and associated risks of contamination and increased cost

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent uses periodic pulsed laser irradiation to form the gettering site. The pulsed nature of the laser allows for controlled energy delivery that achieves the desired effect without the prolonged exposure times required by conventional heat treatment methods

Inventive Principle:

Principle #19Periodic action

3Reliability

If a polycrystalline silicon film is formed on the back surface, then the gettering site is created, but it becomes difficult to apply to large-diameter wafers that require double-side polishing

Engineering Contradiction:

Improvegettering site formationVSAvoidapplicability to large-diameter wafers

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent extracts the gettering site formation process from the back surface and relocates it to the inside of the wafer. By using laser irradiation to create an internal gettering site through multiphoton absorption, the method eliminates the need for back surface modification, making it compatible with double-side polished large-diameter wafers

Inventive Principle:

Principle #2Taking out (Extraction)

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 allows for the efficient formation of gettering sites in a short time, effectively reducing internal stress-induced dislocation and improving device quality by creating a high-quality process-affected layer.

Implementation Method 1

causing a multiphoton absorption process only at a predetermined depth position of the wafer to form a process-affected layer thereat

Methodology Applied

Scientific EffectMultiphoton absorption: Absorption (EM radiation)

Implementation Method 2

the second laser beam is concentrated at a beam-concentration portion in the vicinity of the surface of the wafer to melt the beam-concentration portion

Methodology Applied

Scientific EffectLaser heating: Heating

Implementation Method 3

the beam-concentration portion is then recrystallized

Methodology Applied

Scientific EffectRecrystallization: Crystallisation

Data Source

PatentUS8658516B2Method of producing silicon wafer, epitaxial wafer and solid state image sensor, and device for producing silicon wafer

Publication Date: 2014.02.25 SUMCO CORP

AI summary

An object of the present invention is to provide a method of producing a silicon wafer and a method of producing an epitaxial wafer, which enable easily forming a gettering site in a relatively short period of time and effectively suppressing occurrence of dislocation induced by internal stresses. Specifically, the present invention provides a method of producing a silicon wafer, comprising: irradiating a first laser beam having a relatively long wavelength and a second laser beam having a relatively short wavelength onto a portion of a silicon wafer located at a predetermined depth measured from a surface of the silicon wafer, wherein the first laser beam is concentrated at a portion located at a predetermined depth of the wafer to form a process-affected layer for gettering heavy metals thereat, the second laser beam is concentrated at a beam-concentration portion in the vicinity of the surface of the wafer to melt the beam-concentration portion, the beam-concentration portion is then recrystallized.