Multi-Nano Shell Drift Region Fabrication for Superjunction Devices

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Solution Overview

Problem

The existing methods for fabricating charge balanced drift regions in superjunction semiconductor devices require high thermal budgets and result in low production throughput due to the need for high-temperature, long diffusion processes and the formation of internal voids that disrupt charge balance.

Innovation Solution

A method for creating a multi-nano shell drift region (MNSDR) using a base substrate with a bulk drift layer, forming a vertical cavity, and successively depositing concentric nano shell members of alternating conductivity types, followed by filling residual space with a semi-insulating material to maintain charge balance without high thermal budgets.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high-temperature, long diffusion processes are used to form charge balanced stripes, then the drift region can be formed with alternating conductivity types, but the thermal budget increases and production throughput decreases

Engineering Contradiction:

Improvecharge balance qualityVSAvoidproduction throughput

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The invention changes the fabrication parameters from high-temperature diffusion to low-temperature epitaxial growth, fundamentally altering the process conditions to achieve charge balanced structures without the detrimental thermal budget and time requirements of conventional diffusion methods

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention replaces the thermal diffusion mechanism with a controlled epitaxial growth mechanism, substituting a thermally-driven process with a chemically-controlled deposition process that occurs at lower temperatures and faster rates

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Manufacturing precision

If multiple ion implantation zones are expanded through high-temperature diffusion, then the stripes reach their final sizes, but the process requires 6-10 hours at 1150°C

Engineering Contradiction:

Improvestripe dimension controlVSAvoiddiffusion process time

Core Design Contradiction:

Manufacturing precisionVSLoss of time

Solution Approach 1:

The invention performs preliminary doping during the epitaxial growth process itself, incorporating dopants into the crystal structure as it forms, rather than requiring subsequent high-temperature diffusion to distribute the dopants, thereby achieving the desired doping profiles much faster

Inventive Principle:

Principle #10Preliminary action

3Ease of manufacture

If trenches are filled by epitaxial growth to create charge balanced columns, then the structure is formed, but internal voids are created that disturb charge balance

Engineering Contradiction:

Improvestructure formationVSAvoidcharge balance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The invention applies different doping types and concentrations to different local regions (alternating n-type and p-type layers) within the epitaxial structure, creating the charge balanced pattern through spatial variation of material properties rather than through trench filling that creates voids

Inventive Principle:

Principle #3Local quality

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 enhances production throughput and maintains charge balance without the disturbances caused by internal voids, reducing thermal budget requirements and improving the quality of the drift region.

Implementation Method 1

a) Grow an n-type bulk drift layer (BDL) epitaxially atop the n-type base substrate

Methodology Applied

Scientific EffectEpitaxy: Epitaxy

Implementation Method 2

c) Create, into a top surface of the BDL, a substantially vertical cavity of pre-determined shape and size and with a depth NSHT

Methodology Applied

Scientific EffectAnisotropic etching:

Implementation Method 3

c1) Form, via selective epitaxial growth (SEG), a cavity-shaped doped epitaxial layer upon the vertical cavity

Methodology Applied

Scientific EffectSelective epitaxial growth: Epitaxy

Data Source

PatentUS7892924B1Method for making a charge balanced multi-nano shell drift region for superjunction semiconductor device

Publication Date: 2011.02.22 ALPHA & OMEGA SEMICONDUCTOR INC

AI summary

A method is disclosed for making a substantially charge balanced multi-nano shell drift region (MNSDR) for superjunction semiconductor devices atop a base substrate. The MNSDR has numerous concentric nano shell members NSM1, NSM2, . . . , NSMM (M>1) of alternating, substantially charge balanced first conductivity type and second conductivity type and with height NSHT. First, a bulk drift layer (BDL) is formed atop the base substrate. A substantially vertical cavity of pre-determined shape and size and with depth NSHT is then created into the top surface of BDL. The shell members NSM1, NSM2, . . . , NSMM are successively formed inside the vertical cavity, initially upon its vertical walls then moving toward its center, so as to successively fill the vertical cavity till a residual space remains therein. A semi-insulating or insulating fill-up nano plate is then formed inside the residual space to fill it up.