Impurity Activation Thermal Cycling for Semiconductor Wafer Annealing

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Solution Overview

Problem

Millisecond annealing in semiconductor technology faces challenges in further improving impurity activation rates without increasing impurity diffusion length, particularly with materials like SiGe that have lower thermal resistance, as high temperatures can damage these materials and limit further thermal process enhancements.

Innovation Solution

The method involves repeating a thermal cycle multiple times, with temperature increases from an initial to a higher predetermined temperature, holding at the higher temperature for a short duration, and then decreasing back to the initial temperature, using high temperature-increasing and decreasing rates, and employing heat sources like flash lamps or pulsed lasers to maintain a high activation rate without increasing impurity diffusion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high temperature is applied to improve impurity activation rate, then activation rate increases, but impurity diffusion length increases

Engineering Contradiction:

Improveimpurity activation rateVSAvoidimpurity diffusion length

Core Design Contradiction:

ReliabilityVSLength of moving object

Solution Approach 1:

The patent applies periodic thermal cycling instead of continuous high-temperature processing. The wafer undergoes multiple cycles of rapid heating to high temperature followed by rapid cooling, with each cycle lasting only milliseconds. This periodic action allows impurity activation to occur during the high-temperature phase while the brief duration and rapid cooling prevent significant impurity diffusion.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent uses extremely rapid heating and cooling rates (exceeding 10^6 °C/sec) to 'rush through' the high-temperature state. The thermal process spends minimal time at temperatures where diffusion occurs, effectively skipping the detrimental diffusion phase while still achieving activation during the brief high-temperature window.

Inventive Principle:

Principle #21Skipping (Rushing through)

2Reliability

If high temperature is applied to improve impurity activation rate, then activation rate increases, but thermal damage occurs to low thermal resistance materials like SiGe

Engineering Contradiction:

Improveimpurity activation rateVSAvoidthermal damage

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The rapid thermal cycling creates brief intervals of high temperature sufficient for activation while the majority of the time the material is at lower temperatures, preventing cumulative thermal damage to temperature-sensitive materials like SiGe.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The extremely rapid heating and cooling rates allow the process to quickly pass through the dangerous high-temperature zone, minimizing the exposure time that would cause thermal damage while still achieving the necessary activation effect during the brief high-temperature window.

Inventive Principle:

Principle #21Skipping (Rushing through)

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 allows for improved impurity activation rates in semiconductor devices without increasing impurity diffusion length, even with low thermal resistance materials like SiGe, reducing resistance in transistor regions and enhancing transistor performance while minimizing thermal damage.

Implementation Method 1

increasing a temperature from an initial temperature to a higher predetermined temperature at a temperature-increasing rate of 1.0×10^6 (° C./sec) or more by a flash lamp, a pulsed laser or the like

Methodology Applied

Scientific EffectLight absorption and conversion to thermal energy: Absorption (EM radiation)

Implementation Method 2

holding the temperature at the second predetermined temperature for a second holding period of 50 msec or less

Methodology Applied

Scientific EffectThermal energy retention: Thermal Energy Storage

Implementation Method 3

decreasing the temperature from the second predetermined temperature to the initial temperature at a temperature-decreasing rate of 1.0×10^6 (° C./sec) or more

Methodology Applied

Scientific EffectRapid thermal dissipation: Adiabatic Cooling

Implementation Method 4

an impurity-activating thermal process after a target is subjected to an impurity introduction step

Methodology Applied

Scientific EffectImpurity activation through thermal energy: Annealing

Data Source

PatentUS8017528B2Impurity-activating thermal process method and thermal process apparatus

Publication Date: 2011.09.13 PANASONIC SEMICON SOLUTIONS CO LTD

AI summary

A thermal cycle includes: increasing a temperature from an initial temperature to a temperature T1 at an arbitrary rate R1 (° C./sec); holding the temperature at the temperature T1 for an arbitrary period t1 (sec); increasing the temperature from the temperature T1 to a temperature T2 at a rate R2 (° C./sec) of 1.0×107 (° C./sec) or less; and holding the temperature at the temperature T2 for a period t2 (sec) of 50 msec or less. The thermal cycle thereafter includes: decreasing the temperature from the temperature T2 to the temperature T1 at a rate R1′ (° C./sec) of 1.0×107 (° C./sec) or less; holding the temperature T1 for an arbitrary period t3 (sec); and decreasing the temperature from the temperature T1 to a final temperature at an arbitrary rate R2′ (° C./sec). Such a thermal cycle is successively repeated in a plurality of iterations.