Ion Bombardment Cleaning for Electron Source Contamination

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Solution Overview

Problem

The contamination of the electron source in electron beam writing apparatuses leads to degraded electron beam emission characteristics, requiring lengthy heat treatment for contaminant removal, which reduces the availability of the writing apparatus.

Innovation Solution

A method involving the supply of inert gas to the electron gun chamber, ionization of the gas to produce ions for contaminant removal by bombardment, and terminating the gas supply based on changes in electron beam emission characteristics, allowing for efficient contaminant removal without prolonged downtime.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If heat treatment is used to remove contaminants from the electron source, then the contaminants are removed, but the cleaning time becomes excessively long (over ten hours to several tens of hours)

Engineering Contradiction:

Improveelectron beam emission characteristicsVSAvoidcleaning time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent replaces the thermal field (heat treatment) with an electric field (ion bombardment). By generating ions through gas ionization and using these ions to bombard and remove contaminants from the electron source surface, the cleaning process achieves the same contaminant removal effect as heat treatment but in a fraction of the time (30 minutes to several hours instead of 10+ hours).

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the fundamental parameter of the cleaning mechanism from thermal energy to kinetic energy of ions. By controlling the ion generation conditions (gas type, ionization voltage, ion current), the cleaning efficiency can be adjusted to achieve optimal contaminant removal within a practical time frame while maintaining electron source performance.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the electron gun is subjected to conditioning treatment to prevent abnormal discharge, then abnormal discharge is prevented, but contaminants are deposited on the electron source surface

Engineering Contradiction:

Improveabnormal discharge preventionVSAvoidcontaminant deposition

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent converts the harmful effect of ion bombardment (which could damage the electron source) into a beneficial cleaning effect. By carefully controlling the ion current density and exposure time, the ion bombardment removes contaminants without damaging the electron source structure, thus transforming a potentially harmful process into a useful cleaning mechanism.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent discards the harmful contaminants deposited during conditioning treatment by using ion bombardment to remove them from the electron source surface. This allows the electron source to be recovered to its original clean state, restoring optimal electron beam emission characteristics after conditioning treatment.

Inventive Principle:

Principle #34Discarding and recovering

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 effectively removes contaminants more efficiently than heat treatment, determining the cleaning process termination based on changes in bias voltage or emission current, reducing the cleaning time to approximately 30 minutes to three hours and maintaining apparatus availability.

Implementation Method 1

thermoelectrons emitted from an electron source included in an electron gun of the apparatus are accelerated into an electron beam by an acceleration voltage

Methodology Applied

Scientific EffectThermionic emission: Thermionic Emission

Implementation Method 2

ionizing the inert gas with the electrons to produce ions

Methodology Applied

Scientific EffectIonization: Ionisation

Implementation Method 3

removing contaminants deposited on the electron source by bombardment with the ions

Methodology Applied

Scientific EffectIon bombardment: Ion Beam

Data Source

PatentUS10134559B2Method of cleaning electron source and electron beam writing apparatus

Publication Date: 2018.11.20 NUFLARE TECH INC

AI summary

In one embodiment, a method of cleaning an electron source included in an electron gun for an electron beam writing apparatus includes supplying an inert gas to an electron gun chamber, allowing the electron source to emit electrons, ionizing the inert gas with the electrons to produce ions, and removing contaminants deposited on the electron source by bombardment with the ions, and cutting off the supply of the inert gas based on a change in electron beam emission characteristic of the electron gun.