Laser Gettering for Epitaxial Substrates in Imaging Devices

Solution Overview

Problem

The existing methods for producing epitaxial substrates for solid-state imaging devices are lengthy and costly due to the need for lengthy heat treatment to form gettering sinks, which can also lead to heavy-metal contamination, especially when using double-side polished large substrates like 300 mm wafers.

Innovation Solution

A method involving the use of an ultra-short pulse laser to create gettering sinks by modifying the crystal structure of a semiconductor substrate through multi-photon absorption, allowing for the epitaxial growth of layers and subsequent gettering of heavy metals without the need for extensive heat treatment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If heat treatment is used to form oxygen precipitated portions as gettering sinks, then heavy metal contamination is suppressed, but production time increases and production cost increases

Engineering Contradiction:

Improveheavy metal contamination suppressionVSAvoidproduction time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent replaces the thermal field (heat treatment) with an optical field (laser irradiation) to form gettering sinks. By irradiating the semiconductor substrate with laser beams, oxide precipitates are formed directly without requiring lengthy heat treatment processes, thus suppressing heavy metal contamination while significantly reducing production time.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the formation method of gettering sinks from thermal parameters (heat treatment temperature and time) to optical parameters (laser beam intensity, wavelength, and irradiation time). This parameter transformation enables rapid formation of oxide precipitates with controlled size and distribution, resolving the contradiction between contamination suppression and production efficiency.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If heat treatment is used to form gettering sinks, then heavy metal contamination is suppressed, but production cost increases

Engineering Contradiction:

Improveheavy metal contamination suppressionVSAvoidproduction cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent replaces the thermal field (heat treatment) with an optical field (laser irradiation) to form gettering sinks. By irradiating the semiconductor substrate with laser beams, oxide precipitates are formed directly without requiring lengthy heat treatment processes, thus suppressing heavy metal contamination while significantly reducing production time.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the formation method of gettering sinks from thermal parameters (heat treatment temperature and time) to optical parameters (laser beam intensity, wavelength, and irradiation time). This parameter transformation enables rapid formation of oxide precipitates with controlled size and distribution, resolving the contradiction between contamination suppression and production efficiency.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If amorphous film is formed on back surface to create gettering sinks, then gettering function is achieved, but it becomes difficult to form sinks on double-side polished substrates

Engineering Contradiction:

Improvegettering functionVSAvoidsubstrate compatibility

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent replaces the mechanical/chemical process of forming amorphous films on substrate surfaces with optical field irradiation. The laser beams can penetrate and irradiate the substrate from the front surface, forming oxide precipitates throughout the bulk material without requiring the back surface to be rough or amorphous, thus enabling use of double-side polished substrates.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent transitions from surface-level gettering sink formation (requiring back surface modification) to bulk-level formation by irradiating through the front surface. The laser beams penetrate the substrate and create oxide precipitates at controlled depths, enabling gettering functionality in double-side polished substrates without compromising surface quality.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 simplifies the production process, reduces costs, and effectively suppresses heavy-metal contamination, resulting in solid-state imaging devices with improved imaging properties and low dark leakage current.

Implementation Method 1

condensing the laser beam to an arbitrarily selected (predetermined) portion of the semiconductor substrate, thereby causing a multi-photon absorption process to occur in the portion

Methodology Applied

Scientific EffectMulti-photon absorption:

Implementation Method 2

epitaxially growing at least two epitaxial layers on the semiconductor substrate in which the gettering sink is formed

Methodology Applied

Scientific EffectEpitaxial growth: Epitaxy

Data Source

PatentUS8309436B2Method of producing epitaxial substrate with gettering for solid-state imaging device, and method of producing solid-state imaging device using same substrate

Publication Date: 2012.11.13 SUMCO CORP

AI summary

A method of producing an epitaxial substrate for a solid-state imaging device, comprising: forming a gettering sink by injecting laser beam to a semiconductor substrate through one surface thereof, condensing the laser beam to an arbitrarily selected portion of the semiconductor substrate, thereby causing multi-photon absorption process to occur in the portion, and forming a gettering sink having a modified crystal structure; and epitaxially growing at least two epitaxial layers on the semiconductor substrate in which the gettering sink is formed.